Cellulitis and skin infections explained

What cellulitis is

Cellulitis is an infection of the deeper layers of skin, usually caused by bacteria that get in through a break in the skin — a cut, graze, insect bite, ulcer, patch of eczema or athlete's foot between the toes. It most often affects the lower leg but can occur anywhere. The affected skin becomes red or discoloured, swollen, warm and tender, and the redness tends to spread outwards over hours to days. The area may feel tight and shiny, and some people develop a fever, chills or feel generally unwell. Cellulitis usually affects one side of the body, so redness on both legs at once is more likely to be another cause. Because it can spread and deepen, prompt treatment matters.

Other common skin infections

Cellulitis is one of a family of skin infections. Erysipelas is a more superficial infection with a sharply raised, well-defined edge, often on the face or leg. Impetigo is a very contagious infection, common in children, that causes golden, crusty sores, usually around the nose and mouth. An abscess is a collection of pus under the skin that forms a painful, swollen lump and often needs draining rather than antibiotics alone. Infected wounds, boils and infected insect bites are also common. A rare but extremely serious infection called necrotising fasciitis spreads rapidly and destroys tissue; pain that seems out of proportion to the skin's appearance, rapidly spreading redness and feeling very unwell are red flags for it and need emergency care.

How cellulitis is diagnosed and treated

Cellulitis is usually diagnosed by examining the skin and asking about symptoms; there is no single test, so the diagnosis is based on the appearance and how you feel. Doctors often mark the edge of the redness with a pen so they can see whether it is spreading or settling. Most people are treated with a course of antibiotic tablets and can recover at home, alongside resting and, for a leg, raising it to reduce swelling. Simple pain relief such as paracetamol helps. More severe infection, cellulitis around the eye, infection in someone who is very unwell or has a weakened immune system, or a case that is not improving may need antibiotics through a drip in hospital. It is important to finish the full course of antibiotics even once you feel better.

Warning signs and when to get urgent help

Most cellulitis improves within a few days of starting antibiotics, but some situations need urgent attention. Seek help promptly if the redness is spreading quickly, if you develop a high temperature, shivering or feel very unwell, if you feel confused or drowsy, or if the pain becomes severe and seems worse than the skin looks. Blistering, blackening or skin that is breaking down, a rapidly enlarging area, or symptoms getting worse despite antibiotics are all warning signs. Cellulitis around the eye or on the face needs urgent assessment. These features can point to a more serious or rapidly spreading infection, so it is important not to wait. This is general guidance, and if you are worried you should contact NHS 111, your GP, or 999 if very unwell.

Preventing skin infections

Because cellulitis usually starts where bacteria get through the skin, looking after your skin helps prevent it. Keep cuts, grazes and wounds clean and covered until they heal, and treat conditions that break the skin, such as eczema, leg ulcers and athlete's foot, promptly. Good foot care, moisturising dry skin to stop it cracking, and treating fungal infections between the toes all reduce entry points. People who have had cellulitis before, or who have long-term swelling of a limb (lymphoedema) or poor circulation, are more prone to it and benefit from careful skin care; some who get repeated episodes may be offered preventive antibiotics. Keeping diabetes well controlled and maintaining a healthy weight also help lower the risk.