Cellulitis
Cellulitis is a bacterial infection of the deeper layers of the skin and the fat underneath. The area becomes swollen, warm, tender and discolored, and it spreads. It needs antibiotics, and some presentations need care the same day.
Key facts
Cellulitis at a glance.
Typical signs
Spreading warmth, swelling and tenderness
Common locations
Often lower legs
Expected course
Needs prompt antibiotic treatment
Treatment options
Oral or hospital antibiotics
What is it?
Top things to know about Cellulitis
- It is a bacterial skin infection. Bacteria enter through a crack or wound, sometimes too small to notice.
- It affects deeper skin layers. Inflammation in the dermis and fat causes warmth, tenderness and swelling.
- Lookalikes are common. Dermatitis and venous inflammation can appear similar.
- Diagnosis is mainly clinical. Tests are used selectively; a swollen leg may also need a clot check.
What it looks like
What Cellulitis looks like
Cellulitis is a bacterial infection of the deeper layers of the skin. It causes an area of skin that is warm, swollen, tender and spreading, usually on one lower leg. The border is often not sharply defined. It may come with fever, chills or tiredness. Cellulitis often starts at a break in the skin, such as a cut, insect bite or athlete's foot. Rapid spreading or feeling very unwell needs urgent care.
Swollen leg
Warm, tender, one-sided swelling.
Spreading area
Enlarges over hours to days.
Entry point
Often a cut or cracked skin.
Where it shows up
The lower leg is a common site, but cellulitis can occur elsewhere. The map shows a single example area.
Lower legs
Locations on the lower legs.
On different skin tones
Cellulitis on different skin tones
On lighter skin, cellulitis looks bright red. On brown and Black skin, it may look dark brown, purple or gray, or barely change color. Warmth, swelling, tenderness and spreading are the most reliable signs on every skin tone, and it is helpful to compare with the other leg.
What happens in Cellulitis?
Bacteria enter through a break in the barrier and infect deeper skin and nearby tissue. The inflammatory response causes warmth, swelling, tenderness and an area that may expand.
- Bacteria enter a skin break: A small crack or wound can be an entry point.
- Infection affects deeper tissue: The dermis and nearby tissue become inflamed.
- Swelling and warmth develop: The affected area may expand.
Causes and triggers
What causes Cellulitis
Causes
Why it happens
Cellulitis is a bacterial infection, usually from strep or staph, that gets into the deeper skin through a break.
Risk factors
Raise the odds
- Swelling in the legs
- Obesity
- Diabetes
- Past cellulitis
Triggers
Bring it on or make it worse
- Cuts and scrapes (Well established)
- Athlete's foot cracks (Well established)
- Insect bites (Strong link)
- Surgical wounds (Strong link)
When it usually starts
When it usually starts
Cellulitis
Can develop at any age when bacteria enter deeper skin, often through a break in the barrier.
Daily care
Daily care for Cellulitis
Elevate the limb, properly and often
Raise the affected limb to ease swelling alongside prescribed treatment.
Mark the edge with a pen and the time
Track spreading redness; seek reassessment if it expands or you feel worse.
Clean and cover breaks in the skin
Get bites and punctures assessed.
Check your feet daily
With diabetes or reduced sensation.
Treat athlete's foot and keep treating it
Closes the main entry point.
Ask when to resume prescribed compression after acute cellulitis improves
Compression helps some people prevent recurrent cellulitis after recovery. Do not put stockings over an acutely painful inflamed leg without the treating clinician’s advice.
Avoid: Leaving the leg down all day
Elevation is treatment.
Avoid: Unnoticed cuts and cracks on the feet
Easy to miss with numb feet.
Avoid: Scratching eczema, psoriasis or bites
Every scratch is an entry point.
Avoid: Untreated athlete's foot
The commonest entry point.
Avoid: Delaying treatment
It expands over hours.
Avoid: Using steroid cream instead of assessment for suspected cellulitis
Steroid creams do not treat infection.
Avoid: Leg swelling that is never addressed
Why episodes repeat.
Avoid: Leg ulcers and chronic wounds
A continuously open barrier.
Avoid: Assuming both legs at once is cellulitis
Usually stasis dermatitis.
Avoid: Steroid creams
A steroid cream calms the look of inflamed skin without touching the infection underneath, so it can quieten the appearance while the infection carries on spreading. Cellulitis is mistaken for a rash often enough that this is worth saying plainly. If a leg is hot, swollen, tender and growing, it needs assessing, not a steroid.
Treatments
Treatments for Cellulitis
Acetaminophen and ibuprofen
These cover the pain and bring the fever down while the antibiotics do the work. Taking them regularly for the first couple of days works better than waiting for the pain to peak. They do not treat the infection, and pain that is far worse than the skin looks is a reason to be seen urgently rather than to take more.
Terbinafine cream
Athlete's foot between the toes is the most commonly identified way bacteria get into a leg, and it is one of the few entry points you can genuinely close. An antifungal cream used on the toe webs for two to four weeks, and repeated whenever the skin cracks again, lowers the chance of another episode. It does nothing for the infection you have today.
Antibiotic ointment from the shelf
Cellulitis sits below the surface, deeper than any cream reaches, so an over-the-counter antibiotic ointment cannot treat it. Using one and watching for a day is a common reason people arrive later than they should. It is reasonable on a small fresh cut to keep it clean, and that is all.
Mupirocin
Useful only for the small crusted sore or infected wound that let the bacteria in, not for the cellulitis itself, which is far too deep for a cream to reach. Treating the entry point matters, but it happens alongside antibiotic tablets, never instead of them.
Cephalexin
The usual first choice for ordinary cellulitis, taken four times a day for about five to seven days. It covers the streptococci behind most cases and many staph as well. Antibiotics are not optional here - there is no version of cellulitis that clears without them - and the course is finished even though you feel better in two days.
Doxycycline
Used when MRSA is a concern, when there is pus or a boil involved, or when penicillins do not suit. It is often paired with a second antibiotic because it covers strep less reliably on its own. It is avoided in pregnancy and in young children, and it makes sunburn more likely.
Trimethoprim-sulfamethoxazole
The other main option when MRSA is suspected, particularly with an abscess or a draining wound. Like doxycycline it is often combined with an antibiotic that covers strep properly. It needs care with kidney problems and with some other medicines, so tell the prescriber everything you take.
Clindamycin
An alternative for a genuine penicillin allergy, and it covers both strep and most staph. It causes diarrhoea more often than the others and carries a higher risk of a bowel infection called C. difficile, so it is usually not the first pick. Report diarrhoea that starts during or after the course.
Low-dose preventive antibiotics
For people who keep getting episodes, a small daily dose of penicillin taken for months roughly halves how often they come back. The effect fades once it is stopped, so it works best alongside compression and treating the entry point. Ask about it if you have had two or more episodes.
Outlook
What to expect with Cellulitis
Cellulitis moves fast - over hours rather than weeks, and it needs treatment, not time.
- 1
Starting · Hours 0 to 24
A small area turns tender, warm and swollen, usually on one lower leg, and discoloration follows. Fever, chills or simply feeling unwell can come first.
- 2
Spreading · Days 1 to 3 untreated
The skin tightens and may look shiny or dimpled. Blisters can appear. Fever and illness increase.
- 3
Turning · First 24 to 48 hours of antibiotics
Fever settles first. The skin often looks the same or slightly worse for a day or two, which is expected. What should stop is the edge advancing.
- 4
Settling · Days 3 to 7 of treatment
Discoloration fades. A typical course of oral antibiotics runs about 5 to 7 days, longer if improvement is slow.
- 5
Clearing · Weeks 1 to 3, then months
The skin peels as it recovers, and a darker or lighter mark fades slowly, especially on deeper skin tones. Mild lasting swelling is common. So is another episode, particularly if the limb still swells or the athlete's foot was never treated; for repeated episodes doctors sometimes prescribe a long-term low-dose antibiotic.
Complications
Complications to know about
An abscess underneath
A pocket of pus can form inside the infected area, most often when Staphylococcus aureus is involved or there was a boil or wound to begin with. It shows up as a tender lump that feels boggy or fluid-filled, and it is a common reason antibiotics alone are not working at 48 hours. Pus has to be drained as well as treated, so this is a reason to go back rather than wait.
Swelling and repeat episodes
Each episode damages the lymph channels that drain the limb, so the limb swells more afterwards, and a limb that swells is more likely to be infected again. A previous episode is the strongest predictor of the next one. Compression, daily moisturizer and treating athlete's foot break the loop better than any antibiotic does.
Sepsis
The infection can reach the bloodstream and affect the whole body. The signs are a high fever with shaking chills, confusion or new drowsiness, a racing heart, fast breathing, feeling faint, or passing very little urine. It is uncommon but it is time-critical, so it is an emergency department problem rather than a next-day appointment.
When to get help
When to get help
When to seek care
Suspected cellulitis needs prompt medical assessment. Rapid spread, severe pain, fever, confusion or infection near the eye warrants urgent care.
Questions
Questions you might be asking.
Is cellulitis contagious?
No. The bacteria already live on normal skin, and the infection is in your own deeper tissue. You cannot pass it on, and there is no need to isolate from family. Keep any open, draining wound covered - ordinary wound care.
Why does it look worse after I started antibiotics?
Common in the first 24 to 48 hours. Dying bacteria release material that briefly intensifies the immune reaction, so the area can look more inflamed while you improve. Watch how you feel, whether the fever settles, and whether the marked edge stops. If it is still spreading at 48 hours, go back.
How long will it take to go away?
You should feel better within one to two days, and a typical antibiotic course runs about 5 to 7 days. The skin takes one to two weeks to settle, and peeling is normal. Some swelling and a darker or lighter mark can persist for weeks to months, especially on deeper skin tones.
Do I need to be in hospital?
Most cellulitis is treated with tablets at home. Antibiotics into a vein are used when it is severe or spreading fast, with a high fever or signs of sepsis, when the face or around the eye is involved, when tablets have failed, or with diabetes, poor circulation or a weakened immune system.
Why does it keep coming back?
Usually because the limb still swells and the entry point was never closed. Long-term leg swelling, untreated athlete's foot, and lymph drainage damaged by a previous episode all make the next one more likely. Compression, moisturizing and treating the foot fungus do more than any antibiotic. If it keeps happening, ask about long-term preventive antibiotics.
Is this the same as cellulite?
No, and the similar names cause a lot of confusion. Cellulite is dimpled normal fat beneath the skin, a cosmetic matter. Cellulitis is a bacterial infection of the deeper skin that needs antibiotics and sometimes urgent care.
Sources
Sources and further reading
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