An itchy back can have a variety of causes, including allergies, skin conditions, dry skin and internal diseases, according to Mayo Clinic. Certain substances, such as poison ivy and cosmetics, as well as certain foods can cause allergic reactions and itchy skin.
A skin rash is often a symptom of an allergy caused by allergic contact dermatitis, notes Everyday Health. Allergic contact dermatitis occurs when the immune system reacts to foreign substances that touch the skin. Signs of skin allergies include redness, itchiness and hives. Some of the most common triggers include perfumes and fragrances found in shampoos, soaps, body washes and other household items. Another common allergy is an allergy to nickel found in piercing needles, jewelry, watchbands, zippers and other metal fasteners.
An allergy to certain foods can manifest symptoms immediately or hours after eating, explains WebMD. Mild symptoms can include a red and itchy skin rash, a dry cough, watery eyes, upset stomach, and vomiting. Severe reactions, such as trouble breathing, swollen lips and chest pain, can also occur. Common food allergens include milk, eggs, soy, peanuts and tree nuts. Although nuts may not be main ingredients in certain foods, they may appear unexpectedly on the labels of baked goods, salad dressings and hot dogs.