- Joined
- Jan 6, 2007
Here comes Medusa! (they actually called me "Computer" and "Encyclopaedia" when I was a kid)Medusa (since you seem to actually have some medical knowledge about this!)
Ultraviolet Light
There are three different types of UV-rays.
- UVA (long wave, between 400 and 320nm)
- UVB (medium wave, between 320 and 280nm)
- UVC (short wave, between 200 and 122nm)
UVC does not reach the Earth, so we are not influenced by it.
UVB and UVC damage the DNA directly, UV irradiation of 245 to 290nm is best absorbed by the DNA. UVA doesn't damage the DNA directly, it generates radicals which damage the DNA (and make us age).
For psoriasis, there are two UV-treatments: PUVA (Psoralen + UVA) and UVB (we now have sources that generate mostly at 311 and 312nm, which is less severe for the DNA).
But yes, there is an increased risk for carcinomas, that's why these treatments are not taken lightly and are only implementd in severe cases of psoriasis.
PUVA carries an increased risk for SSC, cutaneous squamous cell carcinoma, (10 to 30 times higher than in the general population) and probably also a higher risk for melanoma. Several studies show that UVB doesn't result in a higher risk for skin cancer, and if it does, than it's only slightly higher. So why do we still do PUVA? It has often proven to be more effective, though with the new UVB sources, UVB is also becoming more effective. Unfortunately, the traditional treatment for psoriasis, immunsuppression with medicaments, also increases the risk for malignant illnesses, e.g. lymphomata.
This article describes everything pretty well, including the DNA-damage that is caused.
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