Testing for skin allergens, also known as allergy skin testing, is a diagnostic procedure used to identify allergens that cause allergic reactions. This test is commonly used to identify allergens in the environment, including pollen, mold, dust mites, and animal dander. 

During skin allergen testing, a small quantity of the allergen is scratched or pricked into the skin. The skin is then examined for a reaction, which may manifest as a raised, red, itchy bump. The test is typically administered on the forearm or back and can last between 20 and 30 minutes. The reaction severity is measured on a scale from 0 to 4, with 4 representing the most severe reaction. The results of the skin test can assist in identifying the allergens responsible for an allergic reaction. 

Serum IgE testing measures the concentration of immunoglobulin E (IgE) antibodies in the blood. IgE is an antibody that the immune system produces in response to allergens. This test can be used to identify allergens responsible for specific allergic reactions. 

For seasonal allergies such as hay fever and allergic rhinitis, serum IgE testing is commonly performed. Additionally, the test can be used to diagnose allergies, such as food allergies. It is essential to note, however, that neither skin allergen testing nor serum IgE testing is perfect; false positives and false negatives can occur. Therefore, these tests should always be interpreted in conjunction with the medical history and physical examination of the patient. A physician or allergist can assist in interpreting the results and developing a suitable treatment plan.