Phototherapy, also sometimes known as light therapy, involves the administration of ultraviolet radiation at certain wavelengths for medical purposes. It is often used as a treatment for psoriasis, particularly when there has been insufficient response to first-line topical treatments.
Targeted vs. Whole-Body Treatments
Targeted phototherapy treatments emit the ultraviolet radiation to the specific areas that are affected and are indicated when a small percentage of the body surface is affected, less than 5%.
Whole-body treatment involves exposure of the entire body – both affected and unaffected areas – to the ultraviolet radiation. This is used in practice when more than 5% of the body surface is affected.
UVA and UVB are both types of ultraviolet radiation present in sunlight, but UVB is more commonly used in phototherapy for psoriasis. It penetrates the surface of the skin and affects the production of skin cells, slowing their growth to help in the treatment of psoriasis.
Administration of UVB therapy involves skin exposure to an artificial source of UVB radiation for a predetermined length of time and regular intervals. This can occur in a medical clinical or at home with a specialized unit.
There are two different kinds of UVB therapy narrow-band and broad-band treatment. Regular sessions of both types of UVB phototherapy treatments are required to achieve the best results.
Natural Sunlight Therapy
It is also possible to use natural sunlight as the source of ultraviolet radiation for phototherapy to treat psoriasis. This is also commonly trialed before the initiation of UVB phototherapy to test the response of UV radiation on the areas affected by psoriasis.
In order to reduce the risk of sunburn and worsening the symptoms of psoriasis, it is recommended to begin therapy with short bursts of sunlight, approximately five to ten minutes daily. The exposure time can then gradually be increased each day while monitoring the tolerance of the skin to the UV dose.
Exposure Time by Skin Type
The phototherapy dose is determined by the length of time that the skin is exposed to the radiation source. The dose for a patient depends on their natural skin type and susceptibility to ultraviolet radiation, as follows:
- Type I: Burns easily, never tans, extremely sensitive skin
- Type II: Burns easily, minimal tan, very sensitive skin
- Type III: Sometimes burns, gradual tan, sun-sensitive skin
- Type IV: Minimal burns, moderate tan, minimally sun-sensitive skin
- Type V: Rarely burns, tans well, sun-insensitive skin
- Type VI: Never burns, deeply pigmented, sun-insensitive skin
Individuals with low skin types require smaller doses of UVB radiation than those with higher skin types, as they absorb the radiation more readily. However, the exact dose for the best effect must be determined for the individual and is established on a trial and error basis.
Adverse Effects of Phototherapy
The adverse effects of phototherapy are primarily due to excessively high doses of UV radiation and include:
- Skin irritation – due to blocked and inflamed pores
- Sunburn – overexposure to UVB radiation
- Skin cancer – high doses can increase risk of skin cancer
- Premature aging – changes to skin show signs of aging