You have given very little information about your complaint.Since you have specified it is large blister,i feel it is important that you consult dermatologist
for thorough workup to rule out 'Blistering Disorders' Like Pemphigus, Pemphigoid
, herpes zoster
, blister due to burns,other photosensitive dermatosis....etc
To give a definitive diagnosis i will need to take a thorough history from you and do physical examination.So i am afraid i can only suggest you to consult a dermatologist
as early as possible.
Hope it helps
Dr.Soumya Nagaraja MD