The term phototherapy literally means the use of light, especially ultraviolet light, to treat medical conditions. Natural sunlight has been known to be beneficial in certain skin disorders for thousands of years, and it is the ultraviolet part of the radiation produced by the sun that is used in phototherapy, in particular the ultraviolet A (UVA) and ultraviolet B (UVB) wavelengths. Patients can be treated with the full UVB spectrum (broadband UVB) or just a small part (narrowband UVB). UVA treatment usually comprises UVA radiation combined with a sensitiser (a chemical that increases the effect of UVA on the skin) called a psoralen (PUVA: Psoralen + UVA). PUVA is also sometimes termed photochemotherapy.
How does phototherapy work?
Ultraviolet light reduces inflammation of the skin and can help in various inflammatory skin disorders. However, although it can cause skin conditions to clear, this is usually temporary and not a cure. PUVA is a more potent form of treatment, so is usually reserved for people who do not respond to UVB.
Psoriasis is the most common condition treated with ultraviolet light, although a variety of other conditions may benefit, including atopic eczema, other forms of dermatitis, polymorphic light eruption, generalised itching, pityriasis lichenoides, cutaneous T cell lymphoma, lichen planus, vitiligo and many others that are less common (disseminated granuloma annulare, morphoea, etc.).
Ultraviolet treatments are usually given in a hospital
outpatient department, two to five times a week, in a walk-in cabinet containing
fluorescent light bulbs. The average course lasts between 15 and 30 treatments.
The starting dose is worked out either by asking how well you tan in sunlight or
by performing a test dose of ultraviolet light on an area of your skin. The
first few treatments will often last less than one minute, and the duration of
exposure to ultraviolet light will gradually increase, up to a number of
The amount of skin exposed to the ultraviolet light will depend primarily on the extent of your condition; for most patients all of the skin is exposed to ultraviolet light, except the eyes (which will be protected by goggles) and male genitalia (which should be covered). A visor or face shield may be worn if your face is not affected by your skin condition.
PUVA treatment involves making your skin extra sensitive to UVA by means of a psoralen, which is either taken orally as tablets, 2 hours prior to each treatment session, or by the application of a solution, lotion or gel directly onto your skin (sometimes in a bath – bath PUVA). If a large area of skin is treated with PUVA you will be required to wear sunglasses that will prevent the exposure of your eyes to natural ultraviolet light for 24 hours from the time of psoralen use.
Your doctor may decide that ultraviolet treatment is not suitable for you if you are very sensitive to sunlight, taking medicines that make you more sensitive to sunlight or if your skin has been damaged by sunlight, sun beds or previous ultraviolet treatments. PUVA treatment may not be used if you have severe liver or kidney disease. PUVA is contraindicated (not recommended) in pregnancy.