Heliotherapy

Heliotherapy is sunlight used as a treatment. Phototherapy is the same idea with lamps. The pleasant surprise in the record is how often the sun was right. Skin can make a hormone from ultraviolet light. That hormone helps bone mineralize and helps immune cells make an antibiotic peptide. A different band of sunlight can lower blood pressure for a short time without touching vitamin D at all. Daylight, even without a tan, sets the clock that organizes sleep. Hospitals noticed pieces of this long before the molecules had names.

The clinical programs of the early twentieth century were not folk customs that medicine later noticed. They had dosing rules, architecture, and published case series, built while tuberculosis filled wards and rickets bent the legs of city children. Skin tuberculosis and surgical bone-and-joint disease were where the sun clinics looked strongest. Open pulmonary tuberculosis was where they were most often refused. Neonatal jaundice is the later, better-measured descendant: a nurse’s observation, then biochemistry, then a treatment still used.

The American chapter is not a footnote. After Finsen’s 1903 Nobel Prize and Rollier’s alpine solaria at Leysin, United States physicians copied the porches, roof wards, window tents, and seashore children’s hospitals. Sea Breeze at Coney Island opened in 1904 for tuberculous bones, joints, and glands. S. Adolphus Knopf described a home window tent in the Journal of the American Medical Association in 1907. Colorado Springs marketed itself as a city of sunshine. Fitzsimons Army Hospital in Denver built heliotherapy platforms after an officer studied Leysin. What they thought they were doing, and what later science showed they were doing, can now be said in the same breath. They were delivering real photons to real tissue. Some of those photons still earn their keep.

A longer history

Sunlight as a health practice is older than the word heliotherapy. Greek medicine already treated sun, wind, and season as part of the body, not as scenery. The Hippocratic essay Airs, Waters, and Places argues that the light and climate of a city shape the people who live there. That is not a dose chart. It is an early insistence that daylight is a biological input. Roman and later European physicians kept the habit of prescribing open air and sun for convalescence, especially for children and for wounds that would not close.

The nineteenth century made the prescription architectural. Florence Nightingale, in Notes on Nursing in 1859, wrote that second only to fresh air, the sick need light, and that a dark house is not a house fit for recovery. She wanted windows the patient could see out of, and sun in the room, not a theory of ultraviolet. The practical effect was the same one later solaria chased with more equipment: get the person into the day.

Arnold Rikli, working at Veldes in the Alps from the 1850s, built a whole cure around sun, air, and water, and was called the sun doctor by people who came to lie in graded light. He was not running a modern trial. He was part of a European turn that treated the sun as a tonic with rules — start small, expose skin, stop before burning. That grammar is still the honest one.

By the 1890s the rickets map had become an argument for light. Theobald Palm, a medical missionary, noticed that rickets was common in the smoky cities of Britain and rare in the sunnier places he had worked. He published the geographical case in The Practitioner in 1890 and urged sunlight as prevention. The molecule was still unnamed. The pattern was already hard to ignore.

Finsen’s lamp

Niels Ryberg Finsen, a Faroese-Danish physician, is the starting point of modern phototherapy as a named science. He used concentrated light, later ultraviolet, against lupus vulgaris — cutaneous tuberculosis that ate faces. His Medical Light Institute opened in Copenhagen in 1896 and treated hundreds. In 1901 he published Phototherapy. In 1903 the Karolinska Institute awarded him the Nobel Prize in Physiology or Medicine for concentrated-light treatment of disease, and in particular of lupus vulgaris. He died the next year.

Finsen lamps spread to Europe and North America. John Harvey Kellogg visited Copenhagen, then built light apparatus at Battle Creek. The method was slow, local, and technical: pressure to blanch the skin, hours on a few square centimeters, months of visits. It was not a day at the beach. It was a demonstration that a measured beam could change a disease the knife had failed.

What Finsen proved, in the language we have now, is that photons can be a drug with a target. Lupus vulgaris is an infection in the skin. Concentrated light, especially the shorter wavelengths, damaged the germs and inflamed the tissue in a way that let it heal. The prize was not given for a mood. It was given for faces that closed.

The lamp also taught a limit that still matters. Dose lived in time, distance, and area. Too little did nothing. Too much burned. Heliotherapy’s best descendant is not a slogan about the sun. It is a clinic that can say how much light, of what color, on what tissue, for how long.

Rollier’s Alps

Auguste Rollier made the sun a regimen for the whole body. In 1903 he opened solaria at Leysin, about thirteen hundred meters in the Swiss Alps, for surgical tuberculosis — bone, joint, gland, peritoneum — not florid lung disease with fever. Exposure began at the feet and advanced by minutes until the child could lie nearly nude in snow light. Rest, a fat-rich diet, and later a work cure sat beside the sun.

His books are the ones people mean when they say there is a book of heliotherapy. La cure de soleil appeared in 1914. The English Heliotherapy followed in 1923 from Oxford. The German volume, Die Heliotherapie der Tuberkulose, came from Springer in 1913 and was enlarged in 1924. Time magazine, in its first year, on the sixth of August 1923, reported more than two thousand surgical-tuberculosis cases over twenty years, and more than eighty percent discharged as cured. Those figures are Rollier’s clinic reports, not a modern randomized trial. They were good enough to send American doctors to Leysin, and to send American children onto roofs.

The method was optimistic and it was cautious at the same time. Rollier did not throw a feverish lung patient into noon sun. He built pigment slowly, watched the pulse, and stopped. Children gained weight. Sinuses dried. Joints that had been scheduled for amputation sometimes did not need it. Sunlight was not the only variable — altitude, food, rest, and hope traveled with it — but the light was the variable he refused to leave out.

Read generously, Leysin is a portrait of what regular outdoor ultraviolet can do for a body that has been kept in the dark: better mineral metabolism, better skin circulation, a child who is no longer a shut-in. Read strictly, it is not proof that sunbathing cures consumption of the lung. Both readings can be true. The generous one is the one the buildings were built for, and it was not foolish.

American solaria

The United States already believed in air. Edward Livingston Trudeau’s Adirondack Cottage Sanitarium at Saranac Lake, opened in 1884, had made rest and cold air a national prescription. Heliotherapy arrived as the visible half of that faith. In June 1904 the New York Association for Improving the Condition of the Poor opened Sea Breeze Hospital at Sea Gate, Coney Island — the first lasting American seashore hospital for surgical tuberculosis in children. Tents went up on the beach. Bed cases were carried to open south porches facing the ocean and stayed out until sundown. Superintendent Alice Page Thomson, after visiting Trudeau, kept an all-year open-air rule.

Orthopedic reports credited sea bathing and sunlight with closing sinuses. Children who could walk played on the sand. A 1905 New York Times visitor wrote that they looked too well to be thought tubercular. Rockefeller money later helped. The building type of those years is the architecture that remains in photographs: porches, balconies, roof decks, and glass pavilions with beds in the light.

Home treatment tried to copy the sanatorium. Knopf’s 1907 window tent framed a tenement window so a patient could sleep in moving air without owning a porch. Yards, roofs, and verandas were the summer prescription. In Colorado Springs, City of Sunshine advertising treated heliotherapy as a regional product. A 1915 brochure claimed the Rockies had far more sunshine than other parts of the country, and that Colorado Springs averaged about seventy percent of possible sunshine. Patients at the Modern Woodmen sanitarium were photographed taking the sun in 1927. F. M. Pottenger wrote on heliotherapy in pulmonary tuberculosis in 1915.

After the First World War, Colonel H. Bruns studied Rollier, then in 1921 started a heliotherapy clinic at Fitzsimons Hospital in Denver. Army records describe a dedicated outdoor ward, then sun porches and enclosed platforms on convalescent pulmonary wards — walls for privacy, open to the sky. The Army’s own caution matches Rollier’s. Do not sun active febrile lung disease. Surgical and selected fibrous cases were the intended group.

Vitamin D, written in skin

The kindest thing sunlight does, and the one we can draw on a blackboard, is to make vitamin D. A molecule in the skin, 7-dehydrocholesterol, absorbs ultraviolet B. It opens into previtamin D3. Body heat then rearranges that into vitamin D3 over hours and days. Michael Holick and colleagues showed this photosynthesis in human skin in Science in 1980, and showed something more elegant than a switch: the skin can store the previtamin and release vitamin D slowly into the blood on a carrier protein. You do not have to stand in the sun until you burn. A modest exposure starts a slow gift.

The liver turns vitamin D3 into 25-hydroxyvitamin D, the number laboratories measure. The kidney, and some immune cells, turn that into the active hormone, 1,25-dihydroxyvitamin D. The hormone’s oldest job is mineral. It raises absorption of calcium and phosphorus from the gut so bone can mineralize. Holick’s 2007 review in the New England Journal of Medicine is the standard map: deficiency softens growing bone into rickets and adult bone into osteomalacia, and low status is common wherever people live indoors, at high latitude, behind glass, or under clothing that never comes off.

The historical proof arrived before the chemistry. In 1919 Kurt Huldschinsky in Berlin healed children’s rickets with a mercury-vapor lamp, the artificial mountain sun, and published the X-ray proof in the Deutsche Medizinische Wochenschrift. In 1921 Alfred Hess and Lester Unger in New York showed that real sunlight did the same thing. Infants exposed on a roof or balcony, diet unchanged, grew calcification at the ends of the long bones within three to four weeks. Hess concluded that the seasons of rickets were the seasons of sunlight. That is still the right sentence.

Glass blocks the wavelengths that do this work. A child in a bright room behind a closed window is not making vitamin D. A child in the same light outdoors is. The National Institutes of Health fact sheet says plainly that ultraviolet B from the sun is a source, and that food and supplements are the other sources, because winter, latitude, skin melanin, age, and sunscreen all change the yield. None of that cancels the mechanism. Skin is a solar organ. It writes a hormone when the right light arrives.

The immune conversation

Vitamin D is not only a bone story. Immune cells carry the vitamin D receptor and the enzyme that activates the hormone. In 2006 Philip Liu and colleagues reported in Science that when human macrophages sense bacterial fragments through a Toll-like receptor, they turn on that enzyme and the receptor, make the hormone locally, and then make cathelicidin — an antimicrobial peptide that can kill Mycobacterium tuberculosis inside the cell. Serum low in 25-hydroxyvitamin D supported that response poorly. Sunlight, by filling the vitamin D reservoir, feeds a defense the immune system already knows how to switch on.

That is a positive finding with a boundary. It is not a claim that sunbathing cures tuberculosis. It is a claim that a nutrient made by ultraviolet light is part of how human innate immunity talks to itself. Later reviews, including Hart and Norval in Frontiers in Immunology in 2021, add the other half of the conversation: ultraviolet also changes circulating immune cells, often in a calming, less inflammatory direction. Dermatology has used that calming for a century. It is why light can quiet some rashes. It is also why large, burning doses are a bad idea — immune quieting is useful in measured amounts and unhelpful if you needed a sharp response that afternoon.

The trial that comes closest to a practical benefit is not a tanning study. It is a vitamin D study, and it belongs here because the vitamin is what skin makes. In 2017 Adrian Martineau and colleagues pooled individual data from twenty-five randomized trials, more than eleven thousand people, in The BMJ. Vitamin D supplementation reduced the risk of an acute respiratory infection. The protection was stronger when people started out deficient, and when the vitamin was given daily or weekly rather than in rare huge doses. Sunlight is the original way to avoid starting out deficient. A pill can stand in when the sun cannot.

Maglio, Paz, and Leoni, writing in 2016, asked whether sunlight’s immune effects are only the ultraviolet suppression everyone already cites. Their answer is no. There are signals that look activating as well as signals that look calming, and vitamin D sits in the activating column for innate antimicrobial defense. A fair summary, and a cheerful one, is this: regular daylight and a vitamin D status that is not collapsed tend to leave the immune system better equipped, not vaguely boosted, and not flattened. Equipped is the word the experiments support.

Vessels and nitric oxide

There is a sunlight benefit that does not wait for vitamin D. Human skin stores nitric oxide in forms that ultraviolet A can release. In 2014 Donald Liu, Richard Weller, Martin Feelisch, and colleagues irradiated healthy volunteers with ultraviolet A — the band that does not make vitamin D — and watched blood pressure fall, nitrate in the blood fall, and nitrite rise. Forearm blood flow increased even when nitric oxide synthase was blocked, which means the light was liberating a store already in the skin, not asking the vessel to make a new batch from scratch.

The effect in that experiment was acute and modest: a measurable drop in pressure after a controlled dose, not a cure for hypertension. It fits an older pattern epidemiologists keep finding and cannot quite finish. Blood pressure and cardiovascular deaths tend to rise in winter and at higher latitude. Vitamin D has been the usual suspect. Weller’s point is that the sun brings a second candidate, a gas released from skin, that acts in minutes.

This is one of the more encouraging modern reasons to like daylight on skin. You do not have to burn. Ultraviolet A arrives in ordinary outdoor light, including times of day when the vitamin D wavelengths are weak. The stores are in the upper epidermis. A walk with sleeves rolled is closer to the experiment than a tanning bed, and it does not require believing that the sun is a panacea. It requires believing a blood-pressure cuff.

The same honesty that belongs to Rollier belongs here. One session in twenty-four volunteers is not a national prevention program. It is a mechanism with a direction: sunlight on skin can relax vessels. People who never go outside miss that signal along with the vitamin D signal. Getting both back is a rational, pleasant prescription.

Sleep, mood, and morning light

The sun does not only write chemicals in skin. It tells the brain what time it is. Morning outdoor light is far brighter, even on a cloudy day, than indoor bulbs, and the clock in the suprachiasmatic nucleus is tuned to that difference. Kenneth Wright and colleagues, in Current Biology in 2013, took people camping in the Rocky Mountains with no electric light. Their melatonin onset and their sleep shifted earlier, into line with sunset and sunrise, within a week. Electric light had been holding their nights late. The sun put the night back.

That is a benefit you can feel without a blood test. People who get outside early often fall asleep more easily and wake more cleanly, because the day had a bright start and the evening was allowed to dim. The light can enter through the eyes while looking at the horizon, the trees, or the street. It does not require looking at the disk. Daylight is the treatment. The disk is not the point.

Mood follows the same clock more often than it follows a mystery. Seasonal depression — low mood that arrives with short days — responds to bright light in the morning in a way psychiatry now treats as a real therapy. Robert Golden and colleagues, in a 2005 meta-analysis in the American Journal of Psychiatry, found bright-light treatment effective for seasonal mood disorder and worth taking seriously beyond winter. The lamps used in those trials are substitutes for a morning the sun would have given for free.

None of this is small. A body that sleeps on time, wakes without a fight, and is not starved of daytime brightness is a body with a better immune day and a better mood. Heliotherapy’s heirs in psychiatry and sleep medicine did not abandon the sun. They measured it, then built lamps for the weeks the sun is late or the office has no window.

Skin that light still treats

Some diseases of the skin are still treated with light on purpose, in clinics, with dosing charts. Psoriasis is the clearest. Ultraviolet B, especially the narrow band around 311 nanometers, slows the overgrowth of skin cells and quiets local inflammation. John Parrish and colleagues introduced a related idea in the New England Journal of Medicine in 1974: psoralen plus ultraviolet A, a photochemotherapy that could clear severe psoriasis. Later, narrowband ultraviolet B became the everyday tool because it works with fewer of the drug effects. Van Weelden and colleagues described that development in the British Journal of Dermatology in 1988. Patients who have lived with plaques know the result as a practical mercy.

The point for a sunlight essay is not that a beach replaces a dermatology booth. A booth measures irradiance. A beach does not. The point is that the same family of wavelengths the sun emits is still prescribed, because skin disease answers to them. Medicine did not retire phototherapy when the tuberculosis wards closed. It kept the part that had a specific, visible target.

Vitiligo, some forms of eczema, cutaneous T-cell lymphoma, and graft-versus-host disease of the skin have all been treated with prescribed ultraviolet in modern clinics. The doses are small relative to a burn and repeated on a schedule. That is Rollier’s grammar with a spectrometer: a little, often, watched. The mood of those clinics is not fear of the sun. It is respect for a tool that still clears lesions other drugs only partly touch.

A person reading this at home should not invent a psoriasis protocol out of noon sun. They should know that dermatology never fully left heliotherapy. It refined it. When a physician sends someone to a light booth, they are continuing Finsen, not canceling him.

Rickets, then streptomycin

Children’s institutions used the same geometry as the adult solaria. Preventoria and open-air schools put desks and cots on roof decks. Vita glass, sold as transmitting ultraviolet, appeared in sun pavilions in the 1920s. Rickets — soft, bowed bones from vitamin D deficiency in dark industrial cities — responded to sunlight for a reason that now has a name. Hess had already shown the bones calcifying. The hormone story caught up later. That part of the sun story is one of the cleanest wins in public health.

Cod-liver oil and sunlight turned out to be two routes to the same molecule. Studies in Vienna after the First World War, sponsored by the Medical Research Council, watched both of them heal war rickets. The practical lesson cities actually used was simpler than a clinic: get children outside, fortify milk, and do not let winter be a nutritional injury. Rickets did not vanish because sunlight was disproved. It faded where sunlight, food, and fortification were allowed to do the job together.

Pulmonary tuberculosis is a different chapter, and it should stay different. Streptomycin, in 1944, and later combination chemotherapy did what porches could not: they killed Mycobacterium tuberculosis in the lung. Sanatoria closed. Solaria became unused roofs. Heliotherapy as a hospital department for consumption ended not because light stopped being useful, but because a better specific arrived for one disease. The light kept its other jobs.

It is easy to tell the story as a humiliation of the sun doctors. The fairer story is a handoff. Chemotherapy took the lung infection. Phototherapy kept jaundice, psoriasis, and a list of skin diseases. Daylight kept the clock. Ultraviolet B kept the vitamin. The roofs emptied. The physics did not resign.

A nurse in Essex

The jaundice story is later, and it is a nurse’s. In the summer of 1956, Sister Jean Ward, in charge of the premature unit at Rochford General Hospital in Essex, wheeled delicate infants into the courtyard. She believed fresh air and sun were better than a stuffy incubator, and she usually had them back inside before consultant rounds.

On a fine day she showed the pediatricians a jaundiced premature baby whose abdomen was pale yellow except for a sharply outlined triangle that was much yellower. R. H. Dobbs asked what she had painted it with — iodine or flavine. She said she thought it was the sun: a corner of sheet had covered the triangle. The rest of the skin had faded. A vial of icteric serum left in daylight later showed a bilirubin drop no one had ordered.

R. J. Cremer, P. W. Perryman, and D. H. Richards published Influence of light on hyperbilirubinaemia of infants in The Lancet on the twenty-fourth of May, 1958. They used both sunlight and a bank of blue fluorescent tubes. Sister Ward was not an author. The observation was hers.

The United States was slow. Franklin, in 1958, worried that photoproducts of bilirubin might be toxic, and that the effect might be too small to replace exchange transfusion. Groups in Brazil, Uruguay, Chile, Italy, and France kept going. Ferreira and colleagues used the word phototherapy in 1960. Jerold Lucey, Mario Ferreiro, and Jean Hewitt published the first widely cited United States controlled study in Pediatrics in 1968. Blue-light phototherapy then became standard nursery care.

The chemistry, worked out later, is not a tan. Visible light, especially blue, isomerizes and oxidizes unconjugated bilirubin in skin to water-soluble products the infant can excrete without conjugation. Photo-oxidation is a minor path. Configurational and structural isomerization do the clinical work. Sunlight can do this. Uncontrolled noon sun also burns. Filtered-sunlight protocols for low-resource nurseries are a twenty-first-century return, with irradiance meters, not a courtyard sheet. Maisels and McDonagh, in the New England Journal of Medicine in 2008, tell the mechanism as settled nursery medicine. The sun started it.

What the buildings were doing

What the American early-1900s buildings were actually delivering, in modern terms, was a mix worth wanting. Ultraviolet-driven vitamin D for rickets and for the immune reservoir that depends on it. A nitric-oxide signal in the skin that can ease pressure. Daylight in the eyes that holds the sleep clock. Possible local effects on skin and superficial infection. Rest, food, and removal from tenement air. A culture that equated a little bronze with getting well, and was more right than a cynical reading allows.

What they were not delivering is a proven, specific, sun-dose protocol for pulmonary tuberculosis that survives comparison with chemotherapy. That limit does not erase the rest. Rollier’s surgical series, Finsen’s lupus work, Hess’s calcifying bones, Sea Breeze’s sinus closures, Ward’s faded triangle, and a modern light booth clearing psoriasis are different claims. They should not be stacked into one miracle. They should be read as a single historical fact with a scientific sequel. For about fifty years, serious hospitals designed themselves around light because some of the targets — skin, bone in children, rickets, bilirubin, and later plaques — really do change when photons arrive. The sequel is that we can now name several of the changes.

The positive case, stated only as far as the papers go, is this. Sunlight on skin makes vitamin D, and vitamin D deficiency is a real injury to bone and a real handicap to one arm of innate immunity. Sunlight on skin can release nitric oxide and lower blood pressure for a while. Sunlight in the eyes, morning outdoor brightness, sets sleep and lifts the kind of mood that tracks the season. Clinics still aim lamps at skin diseases because the lamps work. None of those sentences requires a burn, a stare, or a promise that the sun replaces a doctor.

This is history and physiology, not a protocol. Aurelia does not treat jaundice, tuberculosis, rickets, psoriasis, or high blood pressure. Looking at a high sun is not heliotherapy. The old solaria used skin, shade, time, and a physician’s stop rules. Neonatal phototherapy uses measured blue light and eye shields. Vitamin D can also come from food. Those are not sungazing. They are reasons to like the daylight, to get into it regularly, and to treat it as one of the oldest useful medicines we have.

Sources

1. Hippocrates. Airs, Waters, and Places. Internet Classics Archive.
2. Nightingale F. Notes on Nursing. London: Harrison; 1859. Light, second only to fresh air.
3. Palm TA. The geographical distribution and aetiology of rickets. Practitioner. 1890;45:270–279, 321–342. Reviewed in Hess AF. Rickets, including osteomalacia and tetany. London: Henry Kimpton; 1929.
4. Finsen NR. Phototherapy. London: Edward Arnold; 1901. Nobel Prize in Physiology or Medicine 1903.
5. Huldschinsky K. Heilung von Rachitis durch künstliche Höhensonne. Dtsch Med Wochenschr. 1919;45:712–713.
6. Hess AF, Unger LJ. The cure of infantile rickets by artificial light and by sunlight. Proc Soc Exp Biol Med. 1921;18:298.
7. Rollier A. Heliotherapy. London: Henry Frowde / Hodder & Stoughton; 1923. Also Die Heliotherapie der Tuberkulose. Berlin: Springer; 1913, 2nd ed. 1924.
8. Medicine: Heliotherapy. Time. 6 August 1923.
9. Knopf SA. Aerotherapy and solar therapy in the home treatment of tuberculosis, with description of a window tent. JAMA. 1907;48(3):214–218.
10. Sea Breeze Hospital, Coney Island. Opened 1904 for surgical tuberculosis in children.
11. Cooper AT. Army heliotherapy at Fitzsimons Hospital, Denver, after Bruns’s study of Leysin; clinic 1921.
12. Holick MF, MacLaughlin JA, Clark MB, et al. Photosynthesis of previtamin D3 in human skin. Science. 1980;210:203–205.
13. Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357:266–281.
14. National Institutes of Health, Office of Dietary Supplements. Vitamin D: fact sheet for health professionals.
15. Liu PT, Stenger S, Li H, et al. Toll-like receptor triggering of a vitamin D–mediated human antimicrobial response. Science. 2006;311:1770–1773.
16. Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583.
17. Hart PH, Norval M. More than effects in skin: ultraviolet radiation-induced changes in immune cells in human blood. Front Immunol. 2021;12:694086.
18. Maglio DHG, Paz ML, Leoni J. Sunlight effects on immune system: is there something else in addition to UV-induced immunosuppression? Biomed Res Int. 2016;2016:1934518.
19. Liu D, Fernandez BO, Hamilton A, et al. UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. J Invest Dermatol. 2014;134:1839–1846.
20. Wright KP Jr, McHill AW, Birks BR, et al. Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol. 2013;23:1554–1558.
21. Golden RN, Gaynes BN, Ekstrom RD, et al. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis. Am J Psychiatry. 2005;162:656–662.
22. Parrish JA, Fitzpatrick TB, Tanenbaum L, Pathak MA. Photochemotherapy of psoriasis with oral methoxsalen and longwave ultraviolet light. N Engl J Med. 1974;291:1207–1211.
23. van Weelden H, De La Faille HB, Young E, van der Leun JC. A new development in UVB phototherapy of psoriasis. Br J Dermatol. 1988;119:11–19.
24. Cremer RJ, Perryman PW, Richards DH. Influence of light on hyperbilirubinaemia of infants. Lancet. 1958;271(7030):1094–1097.
25. Dobbs RH, Cremer RJ. Phototherapy. Arch Dis Child. 1975;50(11):833–836. Sister Jean Ward’s 1956 observation.
26. Maisels MJ. Sister Jean Ward, phototherapy, and jaundice. J Perinatol. 2015;35:671–675.
27. Lucey J, Ferreiro M, Hewitt J. Prevention of hyperbilirubinemia of prematurity by phototherapy. Pediatrics. 1968;41(6):1047–1054.
28. Maisels MJ, McDonagh AF. Phototherapy for neonatal jaundice. N Engl J Med. 2008;358:920–928.