How long does narrowband UVB phototherapy take to work for sun allergy?

The treatment gradually exposes the skin to carefully measured UVB under medical supervision. The aim is to make the skin less reactive to sunlight before periods when polymorphic light eruption commonly flares. Early changes may be subtle: fewer new itchy bumps, less redness, or a milder reaction after light exposure. A delayed response does not by itself mean the treatment will not help.

Attend each planned session and follow the clinic’s instructions about medicines, moisturisers, and sun protection. Do not add extra sun exposure to speed the process. Tell the phototherapy team about redness, tenderness, blistering, new medicines, or a history of light sensitivity so the dose can be reviewed safely. Keep a simple record of flare timing and severity.

Contact the clinic promptly for marked burning, blistering, severe pain, or a reaction that is spreading beyond treated skin. Seek urgent help for facial swelling, trouble breathing, faintness, or widespread blistering. Arrange review if repeated sessions bring no meaningful change or if the rash appears without light exposure.

Ask when your response will be assessed, how many sessions are initially planned, what level of redness is expected, and which medicines or skincare products could increase light sensitivity.