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 for trouble breathing, swelling of the tongue or throat, faintness, or a rapidly spreading rash with facial swelling.
Painful blistering, widespread peeling, or a rash involving several moist surfaces, such as the mouth and eyes, also needs emergency assessment.
A purple rash that does not fade when pressed, especially with fever, confusion, severe headache, neck stiffness, or marked illness, requires emergency help.
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 advice if:
A rash begins after starting a new medicine
The skin becomes increasingly warm, swollen, painful, or produces pus
You develop fever or feel unwell with a widespread rash
A rash involves the eyes, mouth, or genitals
Purple spots or bruise-like areas appear without a clear injury
Blisters, ulcers, or rapidly worsening pain develop
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if a rash lasts more than a few weeks, repeatedly returns, disrupts sleep, or occurs with unexplained joint pain, fatigue, digestive symptoms, weight change, or hair and nail changes.
Every sign above is quoted from the sofidex article on Dermatoses - systemic. If you are not sure, err upward — it is always reasonable to be checked.