[1] In contrast to cellulitis, erysipelas is a bacterial infection involving the more superficial layers of the skin, present with an area of redness with well-defined edges, and more often is associated with a fever.

Group A Streptococcus and Staphylococcus are the most common causes of the infection and may be found on the skin as normal biota in healthy individuals.

[13] Predisposing conditions for cellulitis include an insect or spider bite, blistering, an animal bite, tattoos, pruritic (itchy) skin rash, recent surgery, athlete's foot, dry skin, eczema, injecting drugs (especially subcutaneous or intramuscular injection or where an attempted intravenous injection "misses" or blows the vein), pregnancy, diabetes, and obesity, which can affect circulation, as well as burns and boils, although debate exists as to whether minor foot lesions contribute.

Cellulitis in the lower leg is characterized by signs and symptoms similar to those of a deep vein thrombosis, such as warmth, pain, and swelling (inflammation).

This can result in influenza-like symptoms with a high temperature and sweating or feeling very cold with shaking, as the affected person cannot get warm.

Chickenpox and shingles often result in blisters that break open, providing a gap in the skin through which bacteria can enter.

[citation needed] Diseases that affect blood circulation in the legs and feet, such as chronic venous insufficiency and varicose veins, are also risk factors for cellulitis.

[citation needed] Cellulitis is most often a clinical diagnosis, readily identified in many people by history and physical examination alone, with rapidly spreading areas of cutaneous swelling, redness, and heat, occasionally associated with inflammation of regional lymph nodes.

Both are often treated similarly, but cellulitis associated with furuncles, carbuncles, or abscesses is usually caused by S. aureus, which may affect treatment decisions, especially antibiotic selection.

[16] Skin aspiration of nonpurulent cellulitis, usually caused by streptococcal organisms, is rarely helpful for diagnosis, and blood cultures are positive in fewer than 5% of all cases.

[18] Other conditions that may mimic cellulitis include deep vein thrombosis, which can be diagnosed with a compression leg ultrasound, and stasis dermatitis, which is inflammation of the skin from poor blood flow.

Signs of a more severe infection such as necrotizing fasciitis or gas gangrene that would require prompt surgical intervention include purple bullae, skin sloughing, subcutaneous edema, and systemic toxicity.

[16] Misdiagnosis can occur in up to 30% of people with suspected lower-extremity cellulitis, leading to 50,000 to 130,000 unnecessary hospitalizations and $195 to $515 million in avoidable healthcare spending annually in the United States.

[19] Evaluation by dermatologists for cases of suspected cellulitis has been shown to reduce misdiagnosis rates and improve patient outcomes.

When it occurs with acne conglobata, hidradenitis suppurativa, and pilonidal cysts, the syndrome is referred to as the follicular occlusion triad or tetrad.

[28] Antibiotics are usually prescribed, with the agent selected based on suspected organism and presence or absence of purulence,[16] although the best treatment choice is unclear.

[1] Antibiotics choices depend on regional availability, but a penicillinase-resistant semisynthetic penicillin or a first-generation cephalosporin is currently recommended for cellulitis without abscess.

In the United States, an estimated 14.5 million cases annually of cellulitis account for $3.7 billion in ambulatory care costs alone.

Treatment includes cleaning the wound and caring for it properly, the administration of NSAIDs, such as phenylbutazone, cold hosing, applying a sweat wrap or a poultice, and mild exercise.