Cellulitis Signs: How to Tell a Skin Infection From a Rash, and When It's an Emergency

Written by Naurah Gaspard, DNP, FNP-C, FNP-BC · Medically reviewed by Cherlie Joseph, MSN, FNP-BC · Updated November 2026

Cellulitis is a bacterial infection of the deeper layers of skin. The classic signs are redness that spreads over hours to days, warmth, swelling and tenderness, usually on one lower leg, sometimes with fever. It needs antibiotics; mild cases can often be treated with pills at home, but fast spreading, fever with chills, or severe pain out of proportion to how the skin looks needs urgent in-person care.

Early signs of cellulitis

• Red, pink or darker area of skin that is getting bigger
• Warmth when you touch it
• Swelling and tight, shiny skin
• Pain or tenderness
• Often near a break in the skin: a cut, bite, scratch, surgical wound or cracked skin between the toes
• Sometimes fever, chills, feeling tired or swollen, tender lymph nodes

On brown and Black skin, redness may look purple, dark brown or barely visible, so warmth, swelling and pain are more reliable clues. A helpful trick: draw around the edge of the redness with a pen and note the time. If it spreads past the line over the next several hours, that is a sign of active infection and a reason to be seen promptly.

Cellulitis vs look-alikes

Condition	Key clues
Cellulitis	Usually one side; warm, tender, spreading; may have fever
Abscess (boil)	A firm or squishy painful lump with a pus center; often needs draining
Stasis dermatitis	Both lower legs, itchy, brownish, with leg swelling; not very tender
Contact dermatitis	Itchy more than painful; shape matches what touched the skin
Big local bug-bite reaction	Appears within a day of a bite, itchy, usually not spreading after 48 hours
Blood clot (DVT)	Calf swelling and pain, sometimes redness; needs urgent ultrasound

Redness on both legs at once is rarely cellulitis. See our rash identifier guide for more comparisons.

Who gets cellulitis

Cellulitis happens when bacteria, most often strep or staph, get in through a break in the skin. Risk is higher with:

• Athlete's foot or cracked heels, a common and easily missed entry point. See athlete's foot.
• Leg swelling (lymphedema, venous problems) or past cellulitis
• Diabetes, obesity or a weakened immune system
• Eczema, insect bites or scratching
• Recent surgery or injury

How cellulitis is treated

• Antibiotic pills for most mild cases, chosen based on the likely bacteria and whether MRSA is a concern. Courses are usually 5 to 10 days.
• Expect improvement in 1 to 3 days. Redness may look a little worse in the first 24 hours before it improves. If it is clearly spreading after 48 hours on antibiotics, or you develop fever, you need to be re-checked.
• Elevate the area above your heart when resting to reduce swelling and speed healing.
• Treat the entry point: clear up athlete's foot, moisturize cracked skin and control leg swelling.
• Abscesses usually need to be drained in person; antibiotics alone may not be enough.
• IV antibiotics in a hospital are needed for severe infection, fever with rapid spread, or when pills are not working.

For people with repeat cellulitis, compression stockings for leg swelling, daily skin checks and, in some cases, preventive antibiotics can lower the chance of it coming back.

Florida warning: wounds and salt water

Vibrio vulnificus is a bacterium that lives in warm salt and brackish water, like Florida's coast. It can cause a severe, fast-moving wound infection. Florida reported 82 cases and 19 deaths in 2024, a spike linked to Hurricane Helene flooding. It is rare, but the risk is highest for people with liver disease, diabetes or a weakened immune system.

• Stay out of salt or brackish water, and floodwater, if you have a cut, scrape, new tattoo or piercing.
• Cover wounds with a waterproof bandage if you might get wet.
• Wash any wound that touches seawater or raw seafood with soap and clean water right away.
• Wear gloves when handling raw shellfish.
• A wound that becomes very painful, swollen or blistered within a day or two of salt water exposure is an emergency. Tell the clinician about the water exposure.

Frequently asked questions

What does the beginning of cellulitis look like?

A small area of red, warm, tender, swollen skin, often near a cut, bite or crack, that gets bigger over hours to days. Marking the edge with a pen helps you see if it is spreading.

Can cellulitis go away on its own?

Cellulitis usually needs antibiotics. Without treatment it can spread into the blood or deeper tissues, so see a provider rather than waiting.

Is cellulitis contagious?

Cellulitis is generally not spread person to person, though draining wounds should be covered and hands washed well.

Sources

• MedlinePlus: Cellulitis
• American Academy of Dermatology: Cellulitis, how to prevent it from returning
• CBS News Miami: Florida Vibrio vulnificus cases (Florida Department of Health data)

Keep reading

• Rash identifier guide
• Athlete's foot
• Insect bites in Florida
• Browse all conditions and treatments A to Z

This article is for general education and is not a substitute for medical advice. Treatment, including any prescription, is decided by a licensed provider after reviewing your health history. OurTopClinic is not for emergencies; if you have a medical emergency, call 911. OurTopClinic serves adults located in Florida, New Mexico, Oregon and Washington. Learn more at ourtopclinic.com.