Urticaria and erythema are both skin conditions, often appearing together. Erythema is redness of the skin, while urticaria, also known as hives, presents as raised, itchy welts.
Erythema: Redness of the Skin
Erythema is a general term describing redness of the skin. It occurs when the tiny blood vessels near the skin's surface dilate, allowing more blood to flow through. This increased blood flow makes the skin appear red. Many factors can cause erythema, including:
- Sunburn: Exposure to ultraviolet (UV) radiation causes sunburn, resulting in erythema.
- Infection: Infections, like bacterial or viral skin infections, can lead to redness and inflammation.
- Inflammation: Allergic reactions or other inflammatory processes can cause erythema.
- Heat: Exposure to excessive heat can dilate blood vessels, resulting in redness.
Urticaria: Hives or Welts
Urticaria, commonly known as hives, is characterized by raised, itchy welts or plaques on the skin. These welts are typically well-circumscribed (clearly defined) areas of swelling (edema) in the dermis and epidermis. The redness associated with urticaria is a form of erythema. The itching (pruritus) is a significant symptom. Urticaria is often caused by:
- Allergic reactions: Reactions to foods, medications, insect bites, or other allergens can trigger hives.
- Physical stimuli: Pressure, heat, cold, or sunlight can cause physical urticaria.
- Infections: Viral or bacterial infections can sometimes trigger hives.
- Autoimmune diseases: In some cases, urticaria is associated with autoimmune disorders.
Key Differences and Relationship:
While erythema is a general term for redness, urticaria is a specific type of skin reaction that includes erythema as a prominent feature. Essentially, urticaria is a type of skin reaction that always involves erythema (redness) along with edema (swelling) and pruritus (itching). Erythema, however, can occur independently of urticaria as a symptom of many other conditions.
The provided reference states: "Urticaria appears as raised, well-circumscribed areas of erythema (redness) and edema (swelling) involving the dermis and epidermis that are very pruritic (itchy)." This clearly defines urticaria as a specific type of skin condition, inherently involving erythema as a component of its presentation.
