What causes erythema in the skin?

Erythema refers to the redness of the skin that occurs when blood vessels dilate and blood flow increases to a specific area. Vasodilation happens when the smooth muscles of the blood vessels relax, causing them to widen. This increased blood flow brings more red blood cells to the area, which results in inflammation and the characteristic redness associated with erythema.

In contrast, vasoconstriction would reduce blood flow and make the area appear paler, rather than red. Dehydration might affect the skin's overall appearance and health but does not directly cause the dilation of blood vessels leading to erythema. While infection can sometimes result in erythema, owing to inflammation and immune response, the direct and immediate cause of erythema itself is primarily attributed to vasodilation. Therefore, vasodilation is the most accurate description of the mechanism causing erythema in the skin.