Which vesicant causes wheals to appear on the skin?

The vesicant that causes wheals to appear on the skin is typically associated with a type of allergic reaction or irritation, most commonly seen with agents like mustard gas or certain chemical irritants. When these substances come into contact with the skin, they can trigger localized inflammation and the release of histamines, resulting in wheal formation. Wheals are raised, itchy areas that can occur as part of an allergic response.