What kind of reaction occurs with allergic contact dermatitis?

Allergic contact dermatitis is characterized specifically by localized skin irritation that occurs at the site where an allergen or irritant has come into contact with the skin. The primary reaction manifests as redness, swelling, and irritation in that specific area, which can lead to itching and discomfort. This is due to the body's immune response to a substance it identifies as harmful.

While an itchy rash can occur in reaction to allergens, it does not typically spread to the entire body unless the exposure is widespread or there is a systemic reaction, which is uncommon in allergic contact dermatitis. The other options, regarding brittle nails and darkening of the nails, do not relate to the condition either; they typically refer to different types of concerns that can arise from nail health or other forms of skin issues, rather than allergic reactions specifically. Thus, the focus on the localized irritation where the product has been applied is the defining feature that accurately describes allergic contact dermatitis.