Photosensitive eczema - Hx, exacerbates on sun exposed areas
Lupus - butterfly malar rash if acute, else just on sun exposed areas - maybe annular or eczema or psoriasiform, check for circulating ANA
Solar urticaria - rapid onset (mins) short duration (hours)
 
''Polymorphic light eruption'' -
pruritis which starts on sun exposed areas but may spread,
rash (very variable type) develops over 18-24 hours and lasts 7-10 days, small red bumps to larger red / blistering areas - may be itchy or painful
Common - 10% population F>M esp young
occurs in temperate areas (esp spring - as summer progresses occurs less as resistance develops),  familial, also with dark skin,
may occur to artificial light - usually UVA but maybe UVB,
self-limiting if get out of sun, else worsens - trigger uncertain - ? immunological, may limit activity as embarrasing
not infectious, not genetic, no link to skin cancer
Mx - avoid exposure - sunscreen, ?desensitise with UVB, ?? oral steroids (short course) ??? azathioprine
 
Pseudoporphyria - blistering, skin fragility, CKD, Naproxen
Bullous Pemphigoid - elderly, pruritic blisters, flexures, unrelated to sun exposure
 
''Porphyria Cutanea Tarda'' -
skin fragility in sun exposed areas - minor trauma leads to erosions, tense bullae on hands and feet resolve with atrophic scars
30-50 years, male, alcohol, oestrogen tabs, Diabetes, Hep C/HIV,
liver disorder which effects skin - check for HCC
also scarring alopecia, hypertrichosis, morphoea like plaques
Mx - check drugs and co-morbidities, sunblock, venesection, low dose chloroquine