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 your nails or fingertips suddenly look blue or grey and you also have trouble breathing, chest pain, confusion, severe weakness, or fainting.
The colour may reflect low oxygen rather than a nail problem.
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 same-day medical care if redness or swelling around a nail is rapidly spreading, there is pus with fever, or the pain is severe.
Prompt care is also appropriate after a deep cut, a badly crushed finger or toe, a partly torn-off nail, or bleeding that will not stop.
3
Does any of this apply?
Book an appointment
Book a routine appointment if:
A change persists, spreads, worsens, or affects several nails
A nail is painful, repeatedly lifts, or becomes thick and crumbly
You develop unexplained clubbing or spoon-shaped nails
A new dark band appears, widens, becomes irregular, or spreads onto nearby skin
Nail inflammation keeps returning
You have diabetes, poor circulation, or a weakened immune system and develop a nail or surrounding skin problem
Every sign above is quoted from the sofidex article on Nail abnormalities. If you are not sure, err upward — it is always reasonable to be checked.