Allergies occur when the immune system overreacts to normally harmless substances like pollen, dust mites, or certain foods, mistakenly identifying them as threats. This immune response can cause symptoms ranging from mild discomfort to severe, life-threatening reactions. Allergies can emerge at various points throughout an individual’s life, and understanding these timelines is important for recognition and management.
Allergy Onset in Infancy and Childhood
Allergies often begin in infancy, with skin manifestations like eczema (atopic dermatitis) being among the first signs. This condition can appear as early as the first six months of life and may signal a predisposition towards developing other allergic conditions. Children with eczema commonly develop food or respiratory allergies later.
As children grow, food allergies often become apparent. Common food allergens include cow’s milk, eggs, and peanuts, though others like wheat, soy, tree nuts, fish, and shellfish are also involved. While some childhood food allergies, such as those to milk, egg, or wheat, can be outgrown, allergies to peanuts, tree nuts, fish, and shellfish are more likely to persist.
Respiratory allergies like allergic rhinitis (hay fever) and asthma can emerge or worsen during preschool and school-age years. Allergic rhinitis symptoms, such as sneezing, runny nose, and itchy eyes, can develop in children and may peak between the ages of 20 and 40.
Allergy Development in Adulthood
While commonly associated with childhood, allergies can develop or reappear in adulthood, even in individuals with no prior history. Adult-onset allergies can be triggered by new environmental exposures, such as moving to a different climate or acquiring a new pet.
Workplace allergens, changes in diet, or hormonal fluctuations (e.g., during pregnancy or menopause) can also play a role. Common adult-onset allergies include new food allergies, drug allergies, or specific environmental allergies to substances like pollen, dust mites, or mold. Shellfish and tree nuts are common triggers for food allergies that emerge in adulthood.
Key Influences on Allergy Development
The development of allergies is shaped by a complex interaction of genetic predisposition, environmental factors, and lifestyle influences. Individuals with a family history of allergies have an increased likelihood of developing them, with the risk rising significantly if one or both parents have allergies. This genetic tendency, often called atopy, means a person is predisposed to develop allergic conditions, though not necessarily the same specific allergies as their relatives.
Environmental factors also play a substantial role. Exposure to various allergens, such as dust mites, pollens, fungi, and animal dander, can influence allergy development. Air pollution, including gaseous materials like ozone and nitrogen dioxide, and particulate matter from traffic, has been linked to the development and worsening of respiratory allergies.
The “hygiene hypothesis” suggests that reduced exposure to certain microorganisms in early childhood, due to improved hygiene practices and reduced infections, may contribute to an increased risk of allergies. This theory proposes that a diverse range of microbial exposures helps the immune system develop properly, promoting tolerance rather than overreaction. The gut microbiome, the community of microorganisms living in the digestive tract, is particularly important; a lower diversity of gut bacteria in infants has been associated with a higher risk of allergies later in life. Early life exposures to certain microbes can influence immune system development, potentially leading to either tolerance or sensitization to allergens.
Understanding Allergy Symptoms and Diagnosis
Allergy symptoms can vary widely depending on the allergen and the individual, but commonly include sneezing, a runny or stuffy nose, itchy or watery eyes, skin rashes or hives, and sometimes coughing or wheezing. Food allergies might also cause digestive issues like stomach cramps, vomiting, or diarrhea. Symptoms can sometimes be confused with other conditions, making a professional evaluation essential.
If an allergy is suspected, consulting a healthcare professional is advisable for accurate diagnosis. They will typically begin by taking a detailed medical history, including when symptoms occur. Common diagnostic methods include skin prick tests, where small amounts of suspected allergens are applied to the skin to observe for a localized reaction. Blood tests, which measure specific IgE antibodies related to allergens, can also be used to confirm an allergy.