When actor Stephen Fry was busy filming scenes as the British Prime Minister in 24: Live Another Day, a few years ago, he was hospitalised with a swollen ankle.

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It turned out he had the painful skin condition cellulitis, an infection which starts suddenly, affects the deeper layers of the skin, and can be life-threatening if not treated immediately.

Stephen kept his fans posted on Twitter: “Well here’s a how do you do — checking into a hospital.

“Very swollen painful ankle. Doctors seem to take it rather seriously. Cellulitis too.”

He later tweeted: “Being pumped & dripped with antibiotics. Once they’ve done their job MRI tomorrow and hope to be out by the weekend: thanks for good wishes.”

What causes cellulitis?

Cellulitis occurs when bacteria that normally live on the skin without causing problems get inside the skin through a break in the surface such as an insect bite, cut or scratch, a leg ulcer or a crack in dry skin caused by eczema or athlete’s foot.

You’re more at risk of cellulitis if you are obese, have diabetes that’s badly controlled, a weakened immune system through HIV or chemotherapy, poor circulation or lymphoedema, which causes fluid to build up under your skin.

What are the symptoms of cellulitis?

Cellulitis develops quickly and can affect any part of the body, but it’s most common on the lower legs, feet, hands and arms and sometimes on the face around the eyes.

Your skin may become hot, swollen, painful or tender. You may notice the following additional symptoms before or along with those above:

The NHS says that if you notice any of the symptoms below, the infection may have spread to deeper tissue layers, muscles and the blood and could be life-threatening, so you should call 999 or go to A&E immediately:

- Feeling sick, shivering, chills, feeling generally unwell.
- a high temperature (fever) of 38C (100.4F) or above
- a fast heartbeat or fast breathing
- being sick
- diarrhoea
- feeling dizzy or faint
- confusion or disorientation
- cold, clammy, pale skin
- unresponsiveness or loss of consciousness

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What is the treatment for cellulitis?

If you end up in hospital, like Stephen Fry, you’ll be given an intravenous drip or injection of antibiotics.

At home, you’ll have a regular course of antibiotics to take for up to a week, but you may need a longer course.

The NHS also recommends you take the following steps to help yourself recover:

- take paracetamol or ibuprofen for the pain
- raise the affected body part to reduce swelling – for example, if your leg is affected, rest it on pillows or a chair when you're sitting or lying down
- try to regularly move the joint near the affected body part, such as your wrist or ankle, to stop it getting stiff
- drink plenty of fluids to avoid dehydration
- if you usually wear compression stockings – for example, for lymphoedema – avoid these until you've recovered