Understanding cellulitis, causes, risks, management

13^th November 2025 by Dr Alireza Salehzadeh

Understanding Cellulitis: Causes, Risks, and How It’s Managed

Cellulitis is a common bacterial skin infection that affects the lower dermal and subcutaneous layers of the skin. It typically appears as red, swollen, warm and tender skin, often accompanied by fever or systemic symptoms. Because the infection lies deeper than the superficial layers, it can spread rapidly if not treated promptly.

What Happens Beneath the Skin?

The skin is made up of several layers, each of which can be affected by different types of infections. As shown in the work of Bystritsky and Chambers (2018), cellulitis involves the deeper structures—below the epidermis—where bacteria can proliferate and cause widespread inflammation.

Primary risk factors for developing cellulitis

Research has shown the following are the most common risk factors associated with the development of lower limb cellulitis:

1. Chronic oedema of the extremity

Fluid in the peripheries, mainly the legs has been shown to be the highest risk factor for lower limb cellulitis

2. Disruption of the skin barrier

Conditions such as eczema, psoriasis, and generalised dry skin can cause a disruption in the skin barrier and allow bacteria to infect the skin.

3. Obesity (BMI ≥30)

Excess weight has been shown to considerably increase the chances of developing cellulitis.

3. Cancer

Patients with active cancer have a high risk of developing cellulitis

3. Current smoking

Research has shown that smokers are considerably more likely to develop cellulitis than non-smokers

Which Bacteria Cause Cellulitis?

There is ongoing debate regarding the most common causative organisms. DermNet suggests:

Streptococcus pyogenes — ~2/3 of cases

Staphylococcus aureus — ~1/3 of cases

First-Line Treatment Options

According to NICE CKS (2025), recommended antibiotics for uncomplicated cellulitis include:

• Flucloxacillin: This is the first-line antibiotic which is very well-tolerated and has the best coverage for the bacteria causing cellulitis.
• Clarithromycin This is also a well-tolerated and commonly used antibiotic with good coverage of skin bacteria.
• Doxycycline: This is a broad-spectrum antibiotic with excellent coverage of bacteria causing a number of different conditions. It is used in cases where both flucloxacillin and clarithromycin cannot be used.
• Eruthromycin: This is the first choice antibiotic in pregnancy.

Remember cellulitis can worsen rapidly so if your symptoms are not improving with antibiotic therapy, it is paramount that you seek urgent medical advice.

How to Prevent Cellulitis Recurrence

Preventing future episodes involves managing the underlying risks:

• Treat Chronic Oedema: Diuretics can help reduce fluid in the limbs which may be causing limb cellulitis. Compression hosiery and therapy is also useful but it is imperative to not use compression surgery on broken infected skin as can trigger contact dermatitis.
• Stretching the effect: Higher doses (when medically appropriate) may prolong the suppression into later days.
• Protect the Skin Barrier: Aggressive treatment of eczema, dermatitis and any condition causing breaks in the skin.
• Support Healthy Lifestyle Changes: Smoking cessation, reducing alcohol intake and maintaining a healthy weight to improve circulation and reduce infection risk.
• Monitor High-Risk Areas: Regular moisturising and early treatment of cracks or wounds help prevent bacteria entering the skin.

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