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 care for confusion, fainting, trouble breathing, severe weakness, rapidly spreading purple or black skin changes, or severe pain that seems out of proportion to the visible sore.
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
Arrange a medical appointment promptly if you have a thickly crusted sore with an ulcer underneath, especially if it is enlarging, draining pus, or not healing.
Ecthyma often needs antibiotics and can resemble other skin conditions.
Seek same-day medical advice if:
Redness, warmth, swelling, or pain is spreading
New sores are appearing quickly
You develop fever, chills, or feel generally unwell
Red streaks extend from the infected area
The sore is near an eye or on the face
You have diabetes, poor circulation, or a weakened immune system
Treatment has started but symptoms continue to worsen
3
Does any of this apply?
Book an appointment
These symptoms can point to a serious spreading infection rather than routine ecthyma.
The article also says
Dark crust alone can occur with ecthyma.
The concern is a rapid change accompanied by severe pain, spreading skin damage, or significant illness.
Every sign above is quoted from the sofidex article on Ecthyma. If you are not sure, err upward — it is always reasonable to be checked.