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 for a serious eye injury or sudden loss of vision.
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
A stable birthmark does not usually need urgent care.
Seek urgent medical assessment for sudden eye pain, a red eye with blurred vision, halos around lights, severe headache with eye symptoms, or a sudden change in vision.
These are not expected from ordinary congenital dermal melanocytosis and may signal an eye problem requiring prompt care.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if a blue-gray patch has not been assessed before, especially if its cause is uncertain.
Assessment is also appropriate when a mark:
Appears for the first time later in life
Grows quickly or changes shape or color
Becomes raised, painful, itchy, crusted, or prone to bleeding
Is widespread or occurs with developmental or other health concerns
Affects the face, eyelid, or eye
Is causing significant distress
The article also says
New unexplained bruising, particularly with bleeding elsewhere, severe illness, or concern about an injury, should be assessed rather than assumed to be a birthmark.
Every sign above is quoted from the sofidex article on Dermal melanocytosis. If you are not sure, err upward — it is always reasonable to be checked.