erythema
Meaning of erythema: Pressing on the area is the quickest test, since redness from widened vessels fades under a finger and bleeding into skin does not.
Definition of erythema
Erythema is redness of the skin produced by increased blood flow through the small vessels just beneath the surface. It follows sun exposure, minor injury, infection, an allergic or irritant reaction, or forms part of a wider inflammatory skin condition. The word describes an appearance rather than a diagnosis.
Why does skin turn red?
Skin color at any moment depends partly on how much blood sits in the fine network of vessels in its upper layer. Injury, heat, ultraviolet damage and immune activity all release substances that relax the muscle in those vessel walls, so the vessels widen and hold more blood, and the skin reddens and feels warm. Because the blood is still inside the vessels, pressing the area empties them briefly and the color blanches, returning when the pressure lifts. Redness that does not blanch means blood has leaked out into the tissue, which is a different finding altogether and is described as purpura rather than erythema.
What does the pattern suggest?
| Pattern | Appearance | Commonly associated with |
|---|---|---|
| Around a wound or a line | Redness spreading outward with warmth and tenderness | Local irritation or infection |
| Expanding ring with a clearing center | A slowly enlarging patch, often painless | Erythema migrans, the early rash of Lyme disease |
| Target shaped lesions on hands and feet | Concentric rings with a darker center | Erythema multiforme, often following an infection or a drug |
| Tender lumps on the shins | Deep, bruise like nodules rather than a flat rash | Erythema nodosum, linked to infection, drugs and inflammatory disease |
| Confined to sun exposed skin | A sharp border at clothing lines | Ultraviolet exposure or a light sensitive drug reaction |
Why is it sometimes hard to see?
Redness is described from experience with lightly pigmented skin, and on darker skin the same inflammatory change reads as a deeper brown, violet or gray rather than red, or may not be visible at all. Relying on color alone therefore misses inflammation in many people. Warmth, swelling, tenderness, a change in texture and comparison with an unaffected area on the other side of the body carry more weight in those cases, and photographs taken in consistent light help track whether a localized area is enlarging or settling.
Used in a sentence
The nurse documented erythema surrounding the intravenous catheter site.
Good to know
Erythema blanches, or turns pale, under gentle pressure, while a purpuric rash caused by bleeding beneath the skin does not.
Word origin
Where “erythema” comes from
From Greek erythema, meaning redness, related to erythros, meaning red.