Phototherapy is the therapeutic use of ultraviolet irradiation without exogenous photosensitizer. Photochemotherapy (PUVA) is the combined use of the drug psoralen and UVA radiation to achieve an effect not achieved with the individual components alone. Ultraviolet radiation is a small component of the electromagnetic spectrum with a narrow band of radiation from 200-400 nm. The UV spectrum is further divided into UVC (200-280 nm), UVB (280-315 nm) and UVA (315-400 nm).
Different modes it can be administered, listed below;
Broadband UVB therapy and Narrowband UVB therapy
Excimer 308 nm laser treatment
In our country Photochemotherapy PUVA and Narrowband UVB therapy are widely used for treatment of various Dermatological problems
Psoralen + Ultraviolet A (PUVA) photochemotherapy is the photochemical interaction between psoralen and ultraviolet A (UVA) (320 to 400 nm) radiation, which has a beneficial effect in psoriasis and other skin diseases.
Psoralens are naturally occurring tricyclic furocoumarin compounds, present in fruits and vegetables such as limes, lemons, figs and parsnips. The derivative most widely used is 8-methoxypsoralen(8-MOP) principally of plant origin but it is available as a synthetic drug. Trimethyl psoralen (TMP, trioxsalen) which is synthetic is less phototoxic after oral administration and is primarily used for the treatment of vitiligo. Both 8-MOP and TMP are available in oral and topical form.
Orally methoxsalen (8-MOP) is absorbed from the gastrointestinal tract and photosensitivity is present one hour after the dose, reaches a peak at about two hours and disappears after about eight hours.
Principles of PUVA therapy
The rationale for PUVA therapy is to induce remissions of skin diseases by repeated, controlled phototoxic reactions. These reactions occur only when psoralens are photoactivated by UVA.
Repeated exposures are required to clear PUVA responsive diseases and the frequency of treatments is reduced after satisfactory clearing of disease and the last UVA dose is used as a maintenance dose if maintenance treatment is planned. The duration of this maintenance phase and the frequency of treatments depend on the particular disease being treated and its propensity to relapse.
Eye protection with UVA-blocking glasses (B2 Toric glasses) is required from time of exposure to psoralen until sunset that day A sunscreen with an SPF of at least 15 is required for protection from a psoralen phototoxic reaction. Men should also shield their genitalia.
Treatable Diseases by PUVA Therapy
Cutaneous T-cell lymphoma
Graft versus host disease
Polymorphic light eruption
Pityriasis rubra pilaris
Side effects and contraindications
Because PUVA therapy is based on photosensitizing effects, it is contraindicated in patients with photosensitive diseases such as systemic lupus erythematosus and porphyria cutanea tarda. PUVA therapy is also contraindicated in pregnant women PUVA, because of concerns about possible teratogenicity therapy has both acute and chronic side effects. Acute effects include sunburn reactions, nausea, pruritus, headache and dizziness.
The most common chronic side effects of PUVA therapy include premature photoaging, pigmented macules, actinic keratoses, squamous cell carcinoma, basal cell carcinoma and, possibly, anterior cortical cataracts.
Types of UVB
Two types of UVB phototherapy are available: narrowband and broadband and the principles underlying these treatments and protocols used are different.
Narrow band UVB
A potential advance in UVB-based phototherapy has been the introduction of fluorescent bulbs (Phillips model TL-01) that deliver UVB in the range of 310 to 315 nm, with a peak at 312 nm. It has a relatively narrow spectrum of emission and results in a reduction in erythemogenic wavelengths in the 290-305 nm range and 5-6 fold increased emission of the longer UVB wavelengths, thereby resulting in a higher phototherapy index for psoriasis.
Mechanism of action
NB-UVB phototherapy in psoriatics, lowers peripheral natural killer cell activity, lymphocyte proliferation and immune regulatory cytokine production, by both Th1 (IL-2, IFN-g) and Th2 (IL-10) T-cell populations. In vitiligo, it results in stabilization of the depigmenting process the stimulation of residual follicular melanocytes.
Prophylactic low dose NB-UVB has been found to be useful in various predominantly UVA induced photosensitivity disorders like polymorphic light eruption, actinic prurigo, hydroavacciniforme and the cutaneous porphyrias by providing a hardening photoprotective effect.
Broadband UVB phototherapy
High-dose UVB phototherapy using sunlamp bulbs (broadband UVB) was an effective treatment in many patients with psoriasis. High dose means using a treatment schedule aimed at staying close to or above the erythema threshold of the patient throughout the course of treatment.
Conventional UVA1 treatment emits wavelengths mainly between 340 and 400 nm. It is used for the treatment of scleroderma, chronic GvHD, extragenital LSA or sclerodermoid rarities and other disorders affecting the connective tissue.  It is also effective in the treatment of inflammatory skin diseases such as acutely exacerbated atopic dermatitis, urticaria pigmentosa and disseminated granuloma annulare.