For Patients & General Readers

Cellulitis is a common bacterial skin infection that causes redness, warmth, swelling, and pain. It can affect anyone, but people with weakened immune systems or skin injuries are more susceptible. Prompt treatment with antibiotics is important to prevent the infection from spreading and causing serious complications.

Clinical Overview

Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue, typically presenting with localized erythema, warmth, edema, and tenderness. It is most commonly caused by Staphylococcus aureus and Streptococcus pyogenes, often arising from breaches in the skin barrier.

Clinical Presentation

Localized area of erythema that is poorly demarcated and spreads rapidly.
Warmth to the touch over the affected area.
Edema or swelling of the affected skin.
Tenderness and pain upon palpation.
Possible development of vesicles, bullae, or skin necrosis in severe cases.
Systemic symptoms such as fever, chills, and malaise may be present.

Signs & Symptoms

Symptoms (Patient-Reported)

Red, inflamed skin
Warmth in the affected area
Pain or tenderness
Swelling
Fever
Chills
Blisters or rash

Signs (Clinician-Observed)

Erythema with indistinct borders
Edema
Tenderness
Warmth
Possible purulent drainage or bullae

Differential Diagnoses

Condition	Distinguishing Feature
Erysipelas	Characterized by sharply demarcated, raised, erythematous lesions, often with a clear edge, typically affecting the face or lower extremities. Caused predominantly by Streptococcus pyogenes.
Deep Vein Thrombosis (DVT)	Presents with unilateral limb swelling, pain, and warmth, but lacks the characteristic erythema and tenderness of cellulitis. Absence of a clear skin entry point is also a key differentiator.
Contact Dermatitis	Usually presents with pruritus, vesicles, and a more superficial, often eczematous rash with well-defined borders, typically in areas of contact with an allergen or irritant.
Gout	Can cause acute, localized redness, warmth, and swelling, particularly in a single joint (e.g., the great toe). However, it is typically associated with severe joint pain and often a history of hyperuricemia.
Lymphedema	Causes chronic, non-pitting edema, often without the acute inflammation, erythema, and warmth characteristic of cellulitis. May be associated with a history of lymphatic obstruction or surgery.
Insect Bites/Stings	Usually presents as localized pruritic papules or plaques, with surrounding erythema and edema. A history of exposure and the presence of a bite mark are key clues.

Red Flags — Seek Immediate Care

Rapidly spreading erythema
Signs of systemic toxicity (high fever, hypotension, tachycardia)
Development of bullae or skin necrosis
Involvement of the face or periorbital area
Immunocompromised status of the patient

Key Investigations

Blood cultures (if sepsis is suspected)
Complete blood count (CBC) with differential
C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) for inflammatory markers
Wound cultures (if purulent drainage is present or a specific pathogen is suspected)
Imaging (ultrasound or CT scan) to rule out deeper infections like abscess or DVT if indicated.

Management Overview

Management of cellulitis involves prompt initiation of empiric antibiotic therapy targeting common pathogens, typically Staphylococcus aureus and Streptococcus pyogenes. Duration of treatment varies based on severity and response, with close monitoring for improvement and potential complications.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. TruelyserMD does not replace clinical judgement.