UVphototherapy

UV phototherapy, or ultraviolet phototherapy, is a medical treatment that uses controlled exposure to ultraviolet light to treat certain skin disorders. It is delivered in clinics or specialized phototherapy units under the supervision of a physician or dermatologist. Treatments are tailored to the patient and condition, with dosing expressed in fluence or as minimal erythemal dose (MED) for UVB and in terms of UVA exposure for PUVA.

Wavelengths and regimens include broadband UVB, narrowband UVB (around 311–313 nm), and UVA therapy combined with a psoralen photosensitizer (PUVA). Narrowband UVB is the most commonly used form due to a favorable balance of efficacy and safety for many conditions. PUVA is reserved for certain recalcitrant cases or thicker lesions and requires administration of psoralen (or bath psoralen) followed by UVA exposure.

Mechanism of action involves modulation of keratinocyte proliferation and immune responses in the skin. UVB light can suppress inflammatory pathways and alter T-cell activity, while PUVA increases DNA crosslinking in treated cells, contributing to therapeutic effects. The exact mechanisms vary by wavelength and condition.

Indications include moderate-to-severe plaque psoriasis, vitiligo, and, in some cases, atopic dermatitis. It is also used for certain cutaneous T-cell lymphomas and other stubborn dermatoses. Efficacy depends on disease type, skin phototype, and treatment regimen, and phototherapy is often used after topical therapies or when disease is widespread.

Safety and precautions: treatments are generally well tolerated but can cause acute erythema, itching, and dryness. Long-term risks include photoaging and a potential increased risk of skin cancer, particularly with PUVA and high cumulative exposure. Protective eyewear and shielding of non-treated areas are essential, and phototherapy may be contraindicated with photosensitizing medications or in pregnancy.