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
Get urgent or emergency help for a rapidly spreading rash with blistering or peeling, or for breathing difficulty or swelling of the lips, tongue, or throat after using a skin product or medicine.
These are not expected features of pityriasis alba.
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
Seek prompt medical assessment if a skin area becomes hot, swollen, very painful, or starts draining pus, especially with a fever.
These signs are not typical of pityriasis alba and may indicate an infection.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if:
You are unsure what is causing the pale patches
The patches are sharply defined, completely white, or spreading
Hair within the patches also loses colour
The skin is very itchy, inflamed, painful, or repeatedly cracked
Treatment recommended for eczema is not helping
The appearance is affecting your confidence or emotional wellbeing
The article also says
Pityriasis alba itself is not an emergency.
Every sign above is quoted from the sofidex article on Pityriasis alba. If you are not sure, err upward — it is always reasonable to be checked.