Usually one of two things: a dental abscess draining through the gum, or a harmless mucocele - and telling them apart matters.
The abscess brings pain (moderate to severe, throbbing), swelling, and sometimes a bad taste from drainage; some drain quietly while the infection keeps working, and a spreading dental infection can reach the bone and beyond. The mucocele is a soft, painless fluid sac from a blocked salivary gland that often resolves alone. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper .
What to do
Common questions
Why do I get blisters on my gums?
Most gum "blisters" are one of two things - and telling them apart matters. The first is a dental abscess draining through the gum: a pus-filled bump, usually near a problem tooth, and pain is one of the most common reasons patients seek care for it - the pain can be moderate to severe, throbbing or shooting, with swelling almost always present, though some abscesses drain quietly and stop hurting while the infection keeps working. The second is a mucocele: a soft, painless, fluid-filled sac from a blocked minor salivary gland, harmless and often self-resolving. The abscess is the one to respect: a spreading dental infection can track into the bone and beyond, and failure to recognize a systemic infection can lead to serious complications. The rule: any gum bump with pain, swelling, bad taste, or fever is a dentist this week - antibiotics alone do not cure an abscess; the source tooth needs treatment. A painless clear bubble that comes and goes is likely a mucocele - watch it, and get it checked if it persists past a few weeks.