Some skin diseases improve following sunlight exposure. Phototherapy is the use of ultraviolet radiation A or B (UVA 320–400 nm or UVB 280–320 nm) as a treatment (Figure 39.1).

Phototherapy: General Principles

The skin response following exposure to UVA or UVB ranges from mild erythema or burning to blistering. ‘Skin types’ describe the tanning and burning response of individuals to natural sunlight as well as to phototherapy (Table 39.1). During life-long exposure to sunlight, UVA is responsible for skin ageing whereas UVB is responsible for sunburn. Prolonged exposure to natural or other UV radiation (sun beds, repeated phototherapy) can increase the risk of pre-malignant skin lesions and non-melanoma skin cancers. Patients who have received repeated courses of phototherapy should be educated and followed up to identify potential pre-malignant and malignant skin lesions.

Treatment is commenced with a dose of UVA or UVB that causes just visible erythema on that particular individual’s skin (minimal erythema dose). The dose of UVA or UVB is then gradually increased depending on the clinical response. It is important to know what other treatment patients are taking during the course of phototherapy, as some drugs can make patients more photosensitive (e.g. tetracycline, amiodarone).

Phototherapy is considered as a second-line treatment option when topical treatments have failed, when a large body surface area is affected or where treating the individual lesions of the rash with active topical treatment is difficult as the lesions are small and widespread (e.g. guttate psoriasis).

UVB Phototherapy

This is administered within a cabinet containing tubes emitting UVB at a pre-determined dose set by the operator (Figure 39.2). Narrowband UVB (311 nm) has replaced the previous use of broadband UVB phototherapy in many dermatology units.

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