Objective To determine the prognosis for resolution of abnormal cutaneous photosensitivity in patients with chronic actinic dermatitis (also known as the photosensitivity dermatitis and actinic reticuloid syndrome).
Design Historical cohort study involving follow-up of patients for up to 24 years from diagnosis.
Setting A Scottish tertiary referral center for investigation of photodermatosis.
Patients One hundred seventy-eight patients with chronic actinic dermatitis, 62% of a cohort of 285 living patients identified in the Photobiology Unit database.
Interventions Recall for repeated clinical assessment and monochromator phototesting. All patients underwent patch testing when initially assessed; this was repeated at follow-up in a subgroup of patients.
Main Outcome Measures Resolution of abnormal photosensitivity, defined as clinical resolution and return of phototest responses to within normal population limits. In addition, possible prognostic factors for resolution of photosensitivity were examined.
Results The probability of abnormal photosensitivity resolving by 10 years from diagnosis is 1 in 5. Particularly severe abnormal UV-B photosensitivity (minimal erythema dose at 305 ± 5 nm half-maximum bandwidth, 
5.6 mJ · cm-2) and the identification of separate contact allergens in 2 or more patch test batteries are predictors of a poorer prognosis for resolution. Loss of contact allergies was not associated with a different prognosis for photosensitivity resolution. Our findings probably underestimate the probability of resolution, as those referred to a tertiary referral center and willing to attend for follow-up may include a disproportionate number of severely affected patients.
Conclusions Newly diagnosed patients can be told that most of them will improve with appropriate UV/visible light and allergen avoidance and that there is hope that their photosensitivity will completely resolve.
