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 swelling beneath the skin occurs with:
Severe or worsening difficulty breathing
Rapidly expanding swelling of the neck, face, or chest
Blue, grey, or unusually pale lips or skin
Fainting, confusion, or extreme drowsiness
Severe chest pain, especially after an injury
Noisy breathing, choking, drooling, or inability to swallow
A major chest, neck, or facial injury
And for anyone, someone who:
is bleeding heavily and it will not stop with firm pressure
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 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
Prompt assessment is also needed for fever, rapidly worsening pain, spreading redness, skin discolouration, or a person feeling severely unwell.
These can be signs of a deep tissue infection.
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
For a small, already assessed area that is not growing, routine follow-up is usually appropriate.
Seek earlier review if it does not improve as expected, returns, or is joined by new chest or breathing symptoms.
The article also says
Contact a clinician soon if you notice new crackling or swelling after surgery, a chest procedure, dental treatment, forceful vomiting, or a prolonged coughing episode.
This is important even if breathing feels normal, because the source of the air may need investigation.
Every sign above is quoted from the sofidex article on Subcutaneous emphysema. If you are not sure, err upward — it is always reasonable to be checked.