Erythema

What is it?

Erythema is the medical term for redness of the skin caused by increased blood flow in the superficial blood vessels (capillaries) of the dermis. It is one of the most common signs in dermatology and medicine in general, occurring in a wide range of conditions from mild sunburn to serious infections. Erythema itself is not a disease but a sign that indicates an underlying process, most often inflammation. A key feature of true erythema is that it blanches (temporarily disappears) when pressed with a finger or glass slide, distinguishing it from purpura (bleeding into the skin), which does not blanch.

What does it look like?

Erythema has characteristic features:

• Color: Pink to bright red, depending on severity and skin tone
• Surface: The skin surface itself is unchanged — smooth, without scaling or elevation (unless part of a more complex lesion)
• Blanching: Fades temporarily when pressure is applied (diascopy) — this is the defining feature
• Borders: Can be well-defined (as in erysipelas) or diffuse and poorly defined (as in cellulitis)
• Distribution: May be localized (a single area) or widespread (generalized)
• Warmth: Erythematous skin often feels warm to the touch due to increased blood flow

Where does it appear?

Erythema can appear anywhere on the body, with certain patterns suggesting specific conditions:

• Face: Rosacea (central face), lupus erythematosus (butterfly rash across cheeks and nose), sunburn
• Legs: Cellulitis, erysipelas, stasis dermatitis
• Trunk: Drug eruptions, viral exanthems
• Sun-exposed areas: Sunburn, phototoxic reactions
• Contact areas: Allergic or irritant contact dermatitis
• Generalized: Erythroderma (redness covering over 90% of body surface — a dermatological emergency)

Associated features

Erythema may be accompanied by:

• Warmth and tenderness of the affected area
• Swelling (edema) — especially in cellulitis or angioedema
• Pain or burning sensation
• Itching (in allergic or eczematous conditions)
• Fever (in infections such as cellulitis or erysipelas)
• Other skin lesions such as papules, vesicles, or scaling
• Progression or spreading of redness over time

When to see a doctor

Seek medical evaluation for:

• Rapidly spreading redness with fever, warmth, and pain (possible cellulitis or erysipelas — may require antibiotics)
• Generalized redness covering large areas of the body (possible erythroderma — requires urgent evaluation)
• Erythema with difficulty breathing or swelling of lips and throat (possible anaphylaxis — emergency)
• Red rash after starting new medication (possible drug reaction)
• Persistent facial redness that does not resolve
• Red spots that do NOT fade when pressed (this is purpura, not erythema — may indicate a bleeding disorder or vasculitis)
• Any unexplained redness that does not improve within a few days