Cellulitis is an inflammation of the skin and the tissues directly beneath the skin.

It can be caused by a wide range of microorganisms, most commonly bacteria. A beta-haemolytic streptococcus and Staphylococcus aureus are the most common bacteria involved. Over time, more infections are due to strains of bacteria that are resistant to antibiotics, such as methicillin-resistant Staphylococcus aureus (MRSA).

The infection usually occurs when bacteria enter the skin through a cut, a scratch or an insect bite. It can also happen when there is already a skin rash. However it can occur without any visible damage to the skin. A common cause of cellulitis is scratching the skin with fingernails that carry an infection.

Some people are more likely than others to get cellulitis. People are more likely to get cellulitis if they have an injury to the skin and a skin condition like tinea or eczema which also cause the skin to be itchy and are more likely to be scratched.

People are also more likely to get cellulitis if they have swelling in an arm or leg such as with lymphoedema. have poor circulation or have a weak immune system. Having diabetes can put a person at higher risk of cellulitis.

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