Cellulitis is an acute bacterial skin infection that needs same-day medical care. It is common and treatable, but it spreads hour by hour, and left untreated it can lead to serious complications.
In this article we explain exactly what cellulitis is, what causes it, what it looks like, when to call the emergency services, and what treatment involves.
When to seek urgent help
Call 112 or go straight to A&E if you have pain that is far worse than the skin looks, if the redness spreads within hours, if the skin turns dusky or purple, if blisters or black areas appear, if the skin crackles under your fingers, if a red streak tracks from the area towards your body, or if you develop a high fever with shivering, confusion or rapid breathing. These can be signs of necrotising fasciitis or sepsis — both are life-threatening and need hospital treatment within hours.
What is cellulitis?
Cellulitis is an acute bacterial infection of the deeper layers of the skin — specifically the dermis (the deeper layer of skin below the epidermis) and subcutaneous tissue (the layer beneath the skin). The condition differs from superficial skin infections by reaching deeper into the tissue and requiring antibiotic treatment.
A more superficial form of the same infection is called erysipelas. It has a sharply raised border, while cellulitis sits deeper and has a more diffuse edge. The two overlap, are caused by the same bacteria and are treated in much the same way.
Cellulitis should not be confused with cellulite, the dimpled "orange-peel" appearance of the skin. Cellulite is a harmless cosmetic change in the fatty tissue under the skin and has nothing to do with infection. The names look alike, but the conditions have nothing in common.
Cellulitis is not contagious from person to person. It develops when bacteria — typically streptococci or staphylococci — enter the skin through a break or crack in the skin barrier. The same two groups of bacteria cause impetigo, but impetigo stays in the top layer of the skin and does spread by touch.
What does cellulitis look like?
Cellulitis typically presents with the following symptoms:
- Redness and swelling: The affected area is typically red, warm and swollen. The redness often starts locally and spreads over hours to days.
- Pain and tenderness: The area feels painful or tender to the touch.
- Skin changes: The skin may appear tight and shiny. In some cases, blisters or sores may develop on the surface.
- Fever and chills: With a more widespread infection, fever, fatigue and general malaise may occur.
Cellulitis most commonly appears on the lower leg, but can occur anywhere on the body — including the face, arms and feet.
Cellulitis is almost always one-sided. Redness and swelling in both lower legs is much more often venous eczema or stasis dermatitis than infection. Venous eczema develops when blood struggles to return from the legs, and it is treated with compression and emollients — not antibiotics. In many ways it behaves like eczema elsewhere on the body.
Why does cellulitis happen?
Cellulitis develops when bacteria find their way beneath the skin. Even small breaks in the skin barrier can be enough:
How do bacteria get into the skin?
Through a break in the skin barrier. Cuts, scrapes, insect bites and stings, surgical wounds, athlete's foot between the toes and even small cracks or fissures in the skin can all serve as entry points for bacteria. This is why people with poor immune function or underlying skin conditions are at higher risk.
Why do chronic skin conditions increase the risk?
Because they weaken the skin’s natural barrier function. Eczema, dermatitis and other chronic skin conditions make it easier for bacteria to penetrate. People with foot ulcers — particularly those with diabetes — are also at significantly increased risk.
What role do lymphoedema and diabetes play?
Both weaken the body’s defences against infection. Lymphoedema — a condition causing fluid retention and swelling — impairs the lymphatic system’s ability to fight bacteria. Uncontrolled diabetes weakens the immune system and significantly increases the risk of serious bacterial infections.
Who gets cellulitis?
Anyone can develop cellulitis, but certain groups are more vulnerable:
- Adults over 45 and older adults: Incidence is highest in this group and rises with age. With age, immune function declines and the skin’s barrier weakens, while swollen legs become more common.
- Adults with chronic skin conditions or diabetes: A weakened skin barrier and compromised immune system significantly increase the risk.
- People with weakened immune systems: Individuals with HIV/AIDS, cancer or those on immunosuppressive treatment are particularly susceptible.
- Children: Cellulitis is less common in children than in adults, but swelling and redness around an eye (periorbital or orbital cellulitis) is a specific emergency. A child with a red, swollen eyelid needs same-day hospital assessment.
What can you do about cellulitis?
Cellulitis always requires medical treatment. Early diagnosis and appropriate antibiotic treatment are essential to prevent complications:
Antibiotic treatment
Oral antibiotics (tablets) are the standard treatment for mild to moderate cellulitis. In severe cases, intravenous antibiotics (via a drip) may be necessary. Treatment usually lasts 5–7 days for uncomplicated cellulitis, extended only if not improving.
Rest and elevation
Keep the affected area at rest and elevated above heart level to reduce swelling and relieve pain.
Good wound care
Keep the affected area clean and covered with a loose bandage as directed by your doctor. Avoid applying pressure or constriction around the infected area.
Mark the edge of the redness
Draw a line along the edge of the redness with a pen and write the date and time beside it. If the redness spreads past that line, the treatment is not working as it should.
Monitor symptoms
Monitor your temperature and contact your doctor immediately if symptoms worsen — rapidly spreading redness, high fever or confusion. Most people start to improve within 48 hours of starting antibiotics.
Medical classification: Cellulitis is classified as 1B70 in the WHO's International Classification of Diseases (ICD-11) under 'Bacterial cellulitis, erysipelas or lymphangitis'. It is a bacterial infection of the dermis and subcutaneous tissue presenting with erythema and swelling.
Frequently asked questions
Is cellulitis dangerous?
Untreated cellulitis can lead to serious complications including blood poisoning (sepsis), deeper tissue infections and in rare cases amputation. Same-day treatment is essential.
Is redness in both lower legs cellulitis?
Usually not. Cellulitis is almost always one-sided. Redness, swelling and scaling in both lower legs at once is far more often venous eczema, which is treated with compression and emollients rather than antibiotics. Have it assessed rather than assuming either way.
How do I prevent cellulitis?
Clean and cover all skin injuries — even small ones — straight away. Keep skin moisturised to avoid cracks, treat athlete’s foot between the toes, use protective equipment where there is a risk of skin injury, and keep diabetes well controlled.
Can cellulitis come back?
Yes, some people experience recurrent cellulitis, especially if they have underlying risk factors such as lymphoedema or diabetes. Your doctor may recommend preventive antibiotics in such cases.
Think you have cellulitis? Get seen today
Suspected cellulitis needs same-day care. Contact your GP or, out of hours, lægevagten — and call 112 if you have a fever, rapidly spreading redness, or feel very unwell. Use SKIND for follow-up and for skin conditions that are not acute.
Disclaimer: This article is for informational purposes only and does not replace professional medical advice. Always consult a doctor or dermatologist for personal guidance and assessment of skin changes.