Two hand infections get confused constantly, and the distinction decides whether you need tablets or an operating theatre tonight.
- Cellulitis is infection in the skin and the layer under it.
- Septic arthritis is infection inside a joint.
The difference you can test at home: cellulitis hurts to touch, but the joint still moves. Septic arthritis makes even the tiniest passive movement of that one joint agonising… and it destroys cartilage in days.
Cellulitis
Spreading redness, warmth, swelling and tenderness, usually from a small break in the skin — a scratch, a hangnail, a cut, an insect bite.
It is a real problem in a hand, because the skin is thin and the structures underneath are close. It needs antibiotics promptly, not a wait-and-see week.
- Draw around the edge of the redness with a pen, with the time and date. If it’s outside the line in a few hours, that’s rapid spread and needs same-day review
- Elevate the hand. Genuinely above the heart
- Red streaks tracking up the forearm, fever or shivering means go now, not tomorrow
Septic arthritis
Bacteria inside the joint. The enzymes released destroy cartilage rapidly — meaningful damage can occur within days, which is why this is drained surgically rather than treated with tablets and hope.
The picture: ONE joint, swollen and hot, held slightly bent, and exquisitely painful on the smallest movement in any direction. Often a fever, though not always, and often no obvious wound.
Cellulitis: sore to press, but the finger still bends. Septic arthritis: the finger will not let you move it at all.
The commonest route into a finger joint is a puncture over a knuckle, which brings us back to the fight bite — a tooth through a knuckle is the classic cause, and the wound looks trivial.
The others in the same family
Flexor tendon sheath infection — the whole finger swollen evenly, held bent, agony on straightening. A surgical emergency tonight.
Paronychia or felon — infection at the nail fold or in the fingertip pad. Needs draining rather than waiting.
Deep space infection — the palm swollen and boggy with the fingers pushed apart. Also surgical.
The imposter
A single red, hot, swollen finger joint is not automatically infected. Gout looks identical, and so can a flare of inflammatory arthritis.
Nobody separates them by eye. The joint is aspirated, the fluid is examined for crystals and bacteria, and that’s what decides.
Which is exactly why “it’s probably just gout” is a dangerous sentence to say to yourself at 11pm. The two are treated completely differently, and one of them has a clock.
Who needs a lower threshold
Diabetes (see the diabetic hand), immunosuppression, rheumatoid arthritis or anyone on biologics, chemotherapy, and people with lymphoedema. In these groups the usual warning signs can be muted while the infection progresses.
Go to hospital now if
- One joint is swollen and hot, and any movement is severe pain
- Redness is spreading past a line you drew an hour ago
- Red streaks are tracking up the arm
- Fever, shivering, or feeling systemically unwell
- A whole finger is swollen evenly and won’t straighten
- Any wound over a knuckle, especially from a tooth
Hand infections run on hours, not days. The only mistake with real consequences here is waiting until morning.
This is a genuinely time-critical page. If it describes your hand right now, stop reading and go.
Every article on this site is written using the Closing Window Method: name the window your condition runs on, find where you are in it, and act while it’s still open.