allèrgies

Allèrgies are hypersensitivity reactions of the immune system to ordinarily harmless substances called allergens. In many cases allergic reactions are IgE-mediated, but non-IgE mechanisms can also occur. Common allergens include foods such as nuts, milk, and shellfish; environmental agents like pollen, dust mites, mold, and animal dander; drugs; insect venoms; and substances that contact the skin such as nickel and latex.

The process typically involves sensitization, during which the immune system produces allergen-specific IgE antibodies. On re-exposure, these antibodies bind to allergens and trigger release of mediators such as histamine from mast cells, producing symptoms in the skin, nose, lungs, or gut. In severe cases, a systemic reaction known as anaphylaxis can occur, affecting multiple organ systems and requiring urgent treatment with epinephrine.

Diagnosis relies on clinical history and may be supported by tests such as skin prick testing or serum-specific IgE measurements. In some cases, supervised oral food challenges are used to confirm food allergies. Diagnostic accuracy improves with standardized testing and consideration of non-immune causes of symptoms.

Management centers on avoidance of known triggers, education, and an action plan. For potential anaphylaxis, individuals may carry an epinephrine auto-injector and use it promptly. Medications such as oral antihistamines, intranasal steroids, inhaled bronchodilators, or systemic steroids may help with specific symptoms. Allergen immunotherapy is available for selected environmental allergies and, under supervision, oral immunotherapy is used for certain foods.

Prognosis varies; many children outgrow some food allergies with time. Ongoing management includes careful reading of product labels, avoidance of cross-contact, and regular medical follow-up. Allergies differ from intolerances (for example lactose intolerance), which do not involve the immune system.