What type of reaction does an allergy cause?

An allergy specifically involves an abnormal immune response to substances that are typically harmless to most people, such as certain foods, pollen, pet dander, or dust mites. This reaction is characterized by extreme sensitivity in individuals who have been sensitized to a particular allergen.

When someone is allergic to a food, their immune system mistakenly identifies it as a harmful invader and launches an immune response, releasing chemicals such as histamines that lead to allergy symptoms. These symptoms can range from mild, such as hives or nasal congestion, to severe, such as anaphylaxis, which is a life-threatening reaction.

In contrast, the other options do not fit the definition of an allergic reaction. Exposure to cold weather may lead to conditions such as frostbite or hypothermia, lack of exercise affects physical health without invoking an immune response, and excessive sunlight can cause damage like sunburn but is not related to an allergy.