How do I know if it's cellulitis or just irritated skin?

The tell is progression and warmth. Irritated or bruised skin tends to stay put or improve; cellulitis is warm, tender, and visibly spreads over hours, often with the skin feeling tight and swollen, and frequently with fever or feeling unwell. A helpful trick is to draw a pen line around the edge of the redness — if it has clearly moved beyond that line a few hours later, that's a reason to be seen promptly.

Can cellulitis go away on its own?

You shouldn't count on it. Cellulitis is a bacterial infection of the deeper skin, and the standard treatment is a course of antibiotics — most people take them for 7 to 14 days. Caught early and treated, it usually clears completely. Left alone, it can spread to the lymph nodes and bloodstream, so it's not a wait-and-see condition.

Is cellulitis contagious?

Cellulitis itself isn't passed person-to-person the way a cold is — it develops when bacteria get in through a break in your own skin. But the bacteria that cause it (including MRSA) can spread between people, and an open, oozing wound should be kept covered. The infection lives in the deeper skin, not on the surface waiting to jump to someone else.

Cellulitis (A Spreading Skin Infection), Explained

Cellulitis is a common bacterial infection of the deeper layers of the skin — and unlike most skin problems, it's one where time matters. It shows up as an area of skin that is red, warm, swollen, and tender, and it tends to spread. Caught early it's very treatable; ignored, it can become serious. It's estimated that around 14.5 million cases occur in the United States each year (StatPearls), so this is a mainstream problem, not a rare one.

What it is

Cellulitis is an acute bacterial infection of the deep dermis and the tissue just beneath it. Bacteria — most often Streptococcus ("strep") and Staphylococcus ("staph"), including MRSA — get in through a break in the skin: a cut, a scrape, a bug bite, a patch of athlete's foot, a crack from dry skin, or a surgical wound (StatPearls; AAD). Once inside the deeper skin, they multiply and trigger the spreading inflammation you can see and feel.

Adults most often get it on a leg or foot; in children it more commonly appears on the face or neck (AAD).

What it looks and feels like

The classic picture (AAD):

Red (or darker, in deeper skin tones), swollen skin that is warm and tender to the touch.
Skin that feels tight or stretched, sometimes with a slightly shiny look.
Poorly defined edges — the redness blurs outward rather than stopping at a sharp border.
As it worsens: blisters, a red streak heading away from the area, an open sore or pus, and swollen lymph nodes nearby.
Often fever, chills, or just feeling unwell — signs the body is fighting an infection.

The feature that separates cellulitis from ordinary irritation is that it advances. Marking the edge of the redness with a pen and checking a few hours later is a simple way to see whether it's moving.

Why it's worth taking seriously

The reason cellulitis earns its "don't wait" reputation: without treatment, the infection can spread to the lymph nodes and into the bloodstream, which can cause a blood infection or permanently damage lymph vessels (AAD). The good news is that caught early and treated, it usually clears completely without lasting problems.

How it's treated

An oral antibiotic clears most cases, typically taken for 7 to 14 days (AAD treatment). Alongside the medication:

Rest the area and, for a leg, keep it elevated to reduce swelling and speed healing.
Finish the full course even once it looks better — stopping early invites the infection back.
Treat the entry point. Clearing the athlete's foot, dry cracks, or wound that let bacteria in helps prevent it returning.

More severe infections — high fever, rapidly spreading redness, or a person who is very unwell or immunocompromised — may need intravenous antibiotics in hospital.

When to see a doctor — promptly

Cellulitis is a see-someone-today, not a monitor-at-home, condition. Seek prompt medical care if you have:

An area of skin that is red, warm, swollen, and tender — and spreading.
Redness with a fever, chills, or feeling generally unwell.
A red streak spreading from a wound, or pus, blisters, or an open sore.

Get emergency care if the redness is spreading very fast, the pain feels out of proportion to how the skin looks, the skin turns dusky or develops dark patches, or there's swelling of the face or around the eyes — these can signal a deeper, more dangerous infection. People with diabetes, poor circulation, a weakened immune system, or lymphedema should have any suspected cellulitis looked at early, since it can escalate faster.

Because cellulitis is a fast-moving infection, it's outside what a photo tool is built for. A dermatrix.life skin assessment reads uploaded photos for slow, stable skin questions and is informational only, not a diagnosis — spreading redness with warmth or fever needs a clinician who can examine you and prescribe antibiotics, not an app. For the broader question of which rashes are urgent, see When Is a Rash an Emergency?