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
Call emergency services if blue or grey lips, tongue, face, or widespread skin discoloration appears suddenly, especially with:
Difficulty breathing, choking, or inability to speak normally
Chest pain, severe weakness, confusion, unusual drowsiness, or fainting
A suddenly blue, cold, very painful, numb, or weak arm or leg
A suspected medicine, drug, or chemical exposure with breathing or mental changes
Do not stop prescribed medicine without advice unless emergency services tell you to do so.
And for anyone, someone who:
has lips or skin that look pale, blue, grey or blotchy
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 you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Do not wait for the colour to improve or rely only on a home oxygen reading when these symptoms are present.
Seek same-day medical advice if new blue lips or tongue persist, even if you otherwise feel well.
You should also seek prompt advice if blue fingers or toes do not improve after gentle warming, or if they are painful, swollen, or becoming darker.
And for anyone, someone who:
has a wound that is hot, spreading red, or leaking pus
3
Does any of this apply?
Book an appointment
Book a routine appointment if the discoloration repeatedly returns, is gradually spreading, appears during ordinary activity, or has no clear cause.
A persistent blue-grey colour that began after starting a medicine or using a supplement should also be reviewed.
And for anyone, someone who:
has noticed a lump, a mole that has changed, or unexplained weight loss
Every sign above is quoted from the sofidex article on Blue discoloration of the skin. If you are not sure, err upward — it is always reasonable to be checked.