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 emergency help for signs of a severe reaction to a skin product, such as trouble breathing or sudden swelling of the lips, tongue, face, or throat.
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 a prompt assessment if a patch:
Becomes raised, painful, crusted, or persistently itchy
Bleeds, forms an open sore, or changes quickly
Looks very different from your other patches
Develops after starting a medicine that also causes a rash or light sensitivity
These features are not typical of melasma and may have another explanation.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if you are unsure whether the discoloration is melasma, if it is spreading despite careful light protection, or if it affects your wellbeing.
Medical advice is also useful before using prescription-strength products or procedures.
The article also says
Melasma itself is not an emergency.
Every sign above is quoted from the sofidex article on Melasma. If you are not sure, err upward — it is always reasonable to be checked.