Final answer:
Erythema is skin redness caused by the dilation of blood vessels due to inflammation from factors such as contact dermatitis, autoimmune diseases, and infections like those from S. pyogenes. Erythema nodosum is a specific type with red nodules usually on the shins. Eczema can also lead to erythema as part of its inflammatory allergic reaction.
Step-by-step explanation:
Erythema is a condition characterized by redness of the skin due to the dilation of blood vessels in response to inflammation which is one way the body reacts to infections or injuries. This dilation increases blood flow to the impacted area, which makes it appear red and slightly warm. Among the varied causes for erythema are contact dermatitis, which could be from exposure to irritants such as latex, and delayed-type hypersensitivity reactions such as the tuberculin reaction. Additionally, erythema nodosum is another specific type of erythema that leads to red nodules and is associated with inflammation in the subcutaneous fat cells, most commonly on the shins. Conditions such as S. pyogenes infections may lead to conditions like cellulitis and erysipelas, which can also manifest as erythema.
Inflammation responses to autoimmune diseases such as diabetes mellitus type I, multiple sclerosis, and rheumatoid arthritis can also cause erythema. In the case of eczema, which is a skin condition due to an allergic reaction that resembles a rash, erythema can also be present due to the inflammation involved.