Natural sunlight is known to have a beneficial effect on patients with psoriasis. In rare instances, psoriasis patients might find that sunlight actually worsens their condition. Natural sunlight is composed of three types of radiation: ultraviolet (UV) radiation, the visible light spectrum, and infrared radiation. Visible light waves are the only light waves we can see, and we see them as colors of the rainbow. Infrared light cannot be seen. Longer infrared light waves can be felt as heat similar to that of the sun, fire, or a radiator. Short or near infrared light waves cannot be felt. Near infrared, for example, is used by a TV's remote control.
Each category in the light spectrum comprises different components that have their own unique wavelength. The shorter the wavelength, the less energy the light source carries. Just as we measure distance with meters, we measure light waves using a wavelength measurement called nanometers. A wavelength is a measure of 1 nanometer. You would need 1 million nanometers just to make 1 millimeter.
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| Psoriasis Light Therapy |
UV light waves found in sunlight are the source of the beneficial effect on psoriasis. There are three types of ultraviolet rays in sunlight:
- UVC (110-290 nanometers),
- UVB (290-320 nanometers), and
- UVA (320-400 nanometers).
UVB rays are highly effective in treating psoriasis. UVB rays are known as sunburn (B = burning) rays because they represent the portion of sunlight that causes sunburns, and they are mainly responsible for changing skin color, such as when we tan (UVA can also play a role). UVB rays can improve psoriasis on their own or in combination with other treatments. UVA therapy is effective in treating psoriasis when combined with psoralen, but is not very effective when used alone.
Before you undertake a treatment program with phototherapy, it is important to understand how your skin will react to the light. Also, you must let your doctor know if you have any other health problems and what other medications you are on. Some health problems may prohibit you from receiving phototherapy (contraindications). Your doctor could decide that you should not be treated with phototherapy for one of the following reasons:
- You have another disease that causes your skin to be very sensitive to UV light (e.g., systemic lupus erythematosus, polymorphic light eruption).
- The medication(s) you take for your other medical conditions make your skin more sensitive to UV.
- You have a past history of melanoma (the most serious form of skin cancer of the pigment-producing cells in the skin, called melanocytes).
Phototherapy can increase the risk of skin cancer, particularly if used over long periods. If you are having regular phototherapy treatment for your psoriasis, you should also plan for regular skin examinations to be sure no such skin cancers have developed. In addition, if at any time you recognize any non-healing areas on your skin or new growths of concern, arrange to see your doctor. Excess UVL, especially PUVA, will accelerate the appearance of photo-aging of the skin.
Studies have shown that psoralen plus ultraviolet-A (PUVA) light treatment has been linked to the most serious form of skin cancer, cutaneous melanoma. However, this is rare and generally happens only when PUVA treatment is given over a prolonged period.
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| Psoriasis Light Therapy |
Prior to beginning treatment with UV light, your doctor will start therapy based on your skin type. Dr. Thomas Fitzpatrick defined skin type based on the skin's response to sunlight exposure. This method groups skin types from I to VI based on whether the skin burns or tans in response to sunlight exposure. This guideline is one method used to determine the starting dosage of ultraviolet therapy.
A second method your doctor may use to determine your starting dose of ultraviolet radiation is through skin testing. This involves exposing small areas of skin sequentially to different intensities of ultraviolet-B radiation to see the response of your skin. To find out more, you can check out Psoriasis Light Therapy.