What are the signs of a positive patch test?

A positive patch test indicates that a person has an allergic reaction to a substance applied to their skin. The correct answer describes the absence of adverse signs such as redness, itching, or irritation after 48 hours. This indicates that the skin reacted positively to the substance, suggesting that it is safe for use.

In contrast, visible redness and swelling at the application site would indicate a negative outcome, as these symptoms reflect a reaction to the allergen. An immediate allergic reaction upon contact is also a sign of sensitivity rather than a positive patch test result, as patch testing is designed to evaluate reactions that occur after a period of time. Sensitivity to light following the test does not correlate with the results typical of a patch test, which focuses on allergic responses to specific allergens. Thus, the absence of reactions, as described in the correct answer, confirms a negative result, indicating that the individual can likely use the tested product safely.