Comparison

Abscess vs Cellulitis

An abscess is pus in a pocket and needs draining. Cellulitis spreads through the skin and needs antibiotics. How to tell, and when to go the same day.
Written & medically reviewed by the Dermapedia team
At a Glance

Both are bacterial skin infections. One is trapped in a pocket, the other is moving through the tissue — and that difference decides the treatment completely.

An abscess is contained. Pus in one walled-off pocket, with an edge you can feel and a soft centre. It needs to be opened and drained. Antibiotics alone often will not clear it, because the drug struggles to get inside the wall.

Cellulitis is spreading. Bacteria moving through the skin itself, with no pocket, no soft centre, and no clear border. It needs antibiotics. There is nothing to drain, and cutting into it does not help.

They frequently occur together, which is one reason this is a same-day call for a clinician rather than something to work out at home.

Abscess
Contained pus
Cellulitis
Spreading infection
An abscess has an edge you can trace and a centre that gives when you press it. That soft, boggy middle is the pus, and it is the sign that points to drainage rather than antibiotics alone.
Cellulitis has no edge and nothing to drain. The redness fades gradually into normal skin and the whole area is firm rather than boggy. This is the appearance that needs antibiotics — and the reason clinicians draw a pen line around the border, to see whether it is still spreading an hour later.

What you can feel

A defined lump

There is an edge. Press the middle and it gives — soft and boggy, like a small water balloon.

No lump

An area of skin that is red, warm, swollen and tender, but firm throughout. Nothing to press into.

Both
A soft, springy centre is the single most useful sign, and it is what points toward drainage.

The border

Sharp

You can usually trace where it ends.

Blurry and moving

It fades into normal skin, and the area is larger today than it was yesterday.

How it changes

Grows, then points

Builds over days and may come to a yellow or white head.

Spreads outward

Expands across the skin rather than upward.

Both
Drawing a line around the edge with a pen is a standard trick. If the redness passes the line within hours, that is spreading and needs to be seen now.

Where it happens

Anywhere

Especially armpits, groin, buttocks, and around hair follicles.

Most often the lower leg

Also the arms and face. Usually starts where the skin was broken — a cut, a bite, athlete's foot between the toes, or a graze.

Feeling unwell

Sometimes

More likely with larger ones.

Common

Fever, chills, and feeling generally unwell are more typical with cellulitis, and they mean it should be assessed urgently.

Treatment

Drain it.

Numbed, opened, and the pus released. Relief is usually immediate. Antibiotics are added in certain cases, not all.

Antibiotics.

Usually oral, sometimes intravenous if it is severe or not responding. Nothing to drain.

Both
These treatments are not interchangeable. Treating an abscess with antibiotics alone is one of the most common reasons an infection drags on.

How fast it should improve

Immediately after drainage
24 to 72 hours on antibiotics
Both
Cellulitis often looks slightly worse in the first day before it turns. Not improving at all after two to three days means it needs reassessing.

What raises your risk

The pattern
Hair, friction and sweat. Repeated ones in skin folds suggest hidradenitis suppurativa.
The pattern
Any break in the skin, plus swelling in the limb, diabetes, or poor circulation. Untreated athlete's foot is a common and easily missed entry point.
A forearm resting on a clinic table, with a raised, well-defined red swelling on the outer surface and two small yellow points of pus at its centre.
An abscess has an edge you can trace and a centre that gives when you press it. That soft, boggy middle is the pus, and it is the sign that points to drainage rather than antibiotics alone.
A forearm and hand in a clinic, with broad diffuse redness and swelling spreading from the elbow to the wrist, and no defined lump or head.
Cellulitis has no edge and nothing to drain. The redness fades gradually into normal skin and the whole area is firm rather than boggy. This is the appearance that needs antibiotics — and the reason clinicians draw a pen line around the border, to see whether it is still spreading an hour later.

Why you should not try to sort this out yourself

The two look similar early, they often coexist, and the decision — drain or do not drain — is one that needs hands on the skin. An abscess left undrained keeps going. Cellulitis treated with a blade gets worse.

Ultrasound is often used in clinic for exactly this question, because a small pocket of pus deep under an inflamed area is genuinely hard to feel.

Go to urgent or emergency care now if

  • Redness is visibly spreading, or has crossed a line you drew an hour ago
  • You have a fever, chills, or feel shaky and unwell
  • Red streaks are running up the arm or leg
  • The area is on your face, especially around the eye
  • The pain is much worse than the appearance suggests, or the skin is turning dusky, purple, or blistering
  • You have diabetes, a weakened immune system, or lymphoedema

That fifth one matters most. Pain out of proportion to how the skin looks, with rapid change, is the warning sign for a rare but serious deep infection, and it is treated as an emergency.

After it settles

If cellulitis keeps returning in the same leg, the cause is usually an ongoing entry point or swelling. Treating athlete's foot properly, moisturising cracked skin, and managing limb swelling are what prevent the next episode, and they are worth raising at the follow-up.

Questions people ask+
Cellulitis vs abscess — what is the difference?Cellulitis is a bacterial infection spreading through the skin, with no pocket and no clear border, and it is treated with antibiotics. An abscess is pus trapped in one walled-off pocket with a soft centre, and it has to be drained. The two often occur together, which is why this is a same-day call for a clinician rather than a guess at home.
Why does the difference matter?The treatments are opposites. An abscess needs draining, and antibiotics alone often will not clear it. Cellulitis needs antibiotics, and there is nothing to drain.
Can you have both at the same time?Yes, frequently. That is one reason this needs someone with hands on the skin rather than a decision made at home.
How do I know if it is spreading?Draw a line around the edge of the redness with a pen. If the redness passes that line within a few hours, it is spreading and needs to be seen now.
How fast should cellulitis improve on antibiotics?Usually 24 to 72 hours. It often looks slightly worse in the first day before it turns. No improvement at all after two to three days means it needs reassessing.
Where does cellulitis usually start?Most often the lower leg, through a break in the skin — a cut, a bite, a graze, or untreated athlete's foot between the toes. That last one is a common and easily missed entry point.
When is this an emergency?Pain much worse than the skin looks, skin turning dusky or purple, blistering, rapid change, or a fever with spreading redness. Also anything around the eye. Those go to emergency care, not a routine appointment.
Why does my cellulitis keep coming back in the same leg?Usually an ongoing entry point or limb swelling. Treating athlete's foot properly, moisturising cracked skin, and managing swelling are what prevent the next episode.