Pollen from the Willow tree can sometimes act as an allergen, and causes allergic conjunctivitis, rhinitis and asthma. Common symptoms include headaches, itching, wheezing and sneezing among others. A test for immunoglobulin E (IgE) levels in the blood can indicate whether you are allergic or suffering symptoms of another illness. IgE antibodies are commonly found in the lungs, skin and mucous membranes. Histamine and IgE are produced by your body as a reaction to allergens, and increased levels of IgE antibodies generally indicate that you are allergic. As the external symptoms are quite common and can be mistaken for other illnesses, diagnosing the allergy in a timely manner is crucial for treatment.