Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Seek emergency help if blisters occur with trouble breathing, swelling of the face or throat, faintness, or signs of a severe allergic reaction.
Emergency assessment is also appropriate for rapidly spreading blisters with peeling skin, especially when there are painful sores in the mouth, eyes, or genitals.
This is particularly important after starting a new medicine.
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Get same-day medical care if:
Redness, warmth, swelling, or pain is spreading
Pus, red streaks, fever, or chills develop
A blister affects the eye or nearby skin
Pain is severe or the area becomes numb
A burn is deep, large, chemical, electrical, or on the face or genitals
Also seek advice sooner for a foot blister if you have diabetes, reduced feeling, poor circulation, or a weakened immune system.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if blisters keep returning, appear without an obvious injury, cover several areas, or have not improved after about two weeks.
Every sign above is quoted from the sofidex article on Blisters. If you are not sure, err upward — it is always reasonable to be checked.