נדרים ח ב׳
שמש צדקה ומרפא אמר אביי ש"מ חרגא דיומא מסי ופליגא דר"ש בן לקיש דאמר אין גיהנם לעולם הבא אלא הקב"ה מוציא חמה מנרתיקה צדיקים מתרפאין בה ורשעים נידונין בה
“The sun of righteousness, with healing in its rays” (Malachi 3:20)...Abaye said: “We learn from here that the dust of the sun heals”…Rabbi Shimon ben Lakish said, “there is no hell in the world to come. Rather God takes the sun out of its canopy; the righteous are healed by it and the wicked are punished by it” (Nedarim 8b.)
A History of Heliotherapy
In 1903, the Nobel prize for Medicine was awarded to a Dane named Niels Finsen. Finsen had invented a focusable carbon-arc torch to treat – and cure – patients with lupus vulgaris, a painful skin infection caused by tuberculosis. While this was the start of the modern medical use of phototherapy, using the sun as a source of healing is much, much older. Older even than the Talmud, which mentions it in today’s daf.
Perhaps the earliest reference to heliotherapy – that is, using sunlight to heal - is found in Egyptian papyrus records from over 3,500 years ago, which record using the sun, together with ingesting a local weed, to treat skin conditions. The active ingredients of that weed, Ammi majus, were isolated in 1947. These ingredients, together with heliotherapy, were used in the first clinical trials to treat vitiligo, which were conducted, rather fittingly, in Egypt. Further work determined that it was only a narrow part of the sun’s spectrum that was needed to treat vitiligo, psoriasis, and other skin conditions, and so lamps were developed that produced only narrow band ultraviolet light (UVB). These UVB lamps are now a mainstay of treatment for psoriasis.
Sunlight for Healthy Bones
But ultraviolet light – UVB – can also be extremely dangerous. Too much exposure to sunlight will cause skin cancer, as the light produces molecules that directly damage DNA. Here is the great paradox of sunlight – too much of it will burn and can kill – but get the dose right and it is not only curative, but essential for healthy living. Sunlight is needed to produce vitamin D in the skin, and vitamin D is needed to produce healthy bones. Without it, you will develop rickets, a skeletal deformity that is characterized by bowed legs.
Sunlight for a Healthy Immune System
The sun’s light has been shown to have effect the immune system, although many of these effects are only poorly understood.
When some nerve fibres are exposed to sunlight, they release a chemical called neuropeptide substance P. This chemical seems to produce local immune suppression. Exposure to the ultraviolet wavelengths in sunlight can change the regulation of T cells in the body which can also modulate autoimmune diseases.
Sunlight to Treat Melanoma?
While sunlight can cause skin cancer, it has been shown to release a hormone called alpha melanocyte-stimulating hormone. This hormone appears to limit the damage to DNA damage from sunlight and so may actually reduce the risk of melanoma (but don't try this as a treatment yet. It's certainly not ready for prime time.)
Sunlight for Your Mood
Then there’s sunlight for your mood. Seasonal affective disorder – SAD – is caused by a lack of exposure to sunlight, which most affects those living in the northern latitudes in the winter. SAD was first described in 1984 by Norman Rosenthal working at the National Institute of Mental Health but why it happens is still something of a mystery. Rosenthal went on to write several best selling books on SAD and how to beat it. The answer appears to be something to do with sitting in front of a lamp that mimics sunlight (but the evidence that this works is still controversial).
Sunlight for Babies with Jaundice
Sunlight is also a great treatment for babies with neonatal jaundice. This condition is very common and is caused when the baby breaks down the fetal hemoglobin with which it was born. A product of that breakdown is bilirubin, and if this is allowed to build up in the tissues it can cause lethargy, difficultly feeding, and in rare and extreme cases, brain damage. However, sunlight (or more precisely, the blue band of the spectrum at 459nm) breaks down this dangerous bilirubin molecule into a harmless one called biliverdin. So the best treatment for a newborn baby with mild jaundice is to put them out in the sun. (Failing that, or if the degree of jaundice is not mild, you can consider phototherapy in the hospital.)
Sunlight for Infectious Diseases
We don't treat infectious diseases with sunlight any more. But it wasn't always that way. Less than eighty years ago sunlight was recommended as a therapy for some patients with tuberculosis. The authors, writing in the journal Diseases of the Chest were cautious:
Even in those cases where the sun can be of great value, it is in no sense a specific cure for any manifestation of tuberculosis. Rest, good food, and fresh air, are still the fundamentals in treating all forms of the disease; and the sun, where it should be used, is only a valuable adjutant...Heliotherapy is not indicated in all cases of tuberculosis. The majority of patients with this disease should never use it...It is not a sure cure for any type of tuberculosis, but is often, especially in some of the extrapulmonary cases, a very valuable—or even necessary—aid.
In today's daf, Abaye noted that the sun can heal, and Rabbi Shimon ben Lakish (a.k.a Resh Lakish) taught that the sun can both reward and punish. Their insights were more correct than they could ever have guessed.