What is a common sign of an allergic reaction to medication?

A skin rash or hives is a hallmark sign of an allergic reaction to medication. Allergic reactions occur when the immune system mistakenly identifies a medication as a harmful substance, triggering an immune response. This can manifest in various ways, but skin-related symptoms, such as rashes, hives, or itching, are among the most common. These dermatological reactions can vary in severity, from mild localized hives to widespread rashes that can pose more serious risks.

In contrast, the other options typically do not align with the classic presentations of allergic reactions. Increased appetite is not an indication of an allergic response and is more suggestive of different physiological or psychological factors. Fatigue and sleepiness are general symptoms that can relate to numerous conditions, including the side effects of certain medications rather than an allergic reaction specifically. Improved concentration is not associated with allergic reactions; in fact, many medications that cause allergic symptoms can lead to distraction or discomfort, further impacting cognitive function.