Allergies come about when your body confuses a generally benign substance as being harmful to the body. The immune system overreacts and allergic symptoms are experienced. Allergies may be caused by exposure to something in the environment, something in your diet, or something you've come into direct contact with. For an allergy that causes a non-itchy rash, the latter two are the main suspects.
Make a log entry describing your overall physical and mental state of being. The rash you're experiencing may be the most obvious, but may not necessarily be the only symptom you have. You may simply be dismissing much milder symptoms. Make a note of any fatigue, bloating, gas, constipation or diarrhoea, lightheadedness, trouble concentrating, irritability, headaches, muscle aches or weakness.
Eliminate all foods from your diet which contain wheat, gluten, oats, soy, eggs, milk, nuts, corn and food additives for the next 7 to 30 days. This will mean abstaining from processed, take out, and fast foods for this period. Stick to a diet of home prepared fresh fruits and vegetables, rice and rice based products such as rice milk, beans, and meats (with the exception of hot dogs and luncheon meats). Be mindful of the ingredients you use to season your food. Read nutritional labels very carefully to make certain they do not contain banned food substances.
Keep a daily log of your food intake and update your physical and mental status. Make a note of any changes. If your rash has not disappeared and stayed away after 30 days on this diet, it's likely not a reaction to something in your diet. If the rash has disappeared, try to determine which food you may cause the allergic reaction.
Maintaining your log entries, reintroduce one eliminated food back into your diet for a day and record your body's reaction to it. Symptoms may reappear after only a few moments or may take the entire day. The following day, abstain from the previous day's reintroduced food and reintroduce another eliminated food. Again record your body's reaction. Continue this pattern until you have tested your reaction to all the eliminated foods. DO NOT reinstitute multiple eliminated foods back into your diet at the same time.
Reflect on any new product you may have purchased in the past 30 days. A new soap, cleaning product, clothes (check the material), detergent, etc. Try not exposing yourself to that product and observe your body's reaction.
Think about the environments you've been in. What products and substances have you come into contact with there? If you have a pet, consider the possibility that you may be having a reaction to your pet's saliva. Again, avoid contact and monitor your reaction.
Consider the location of your rash and the products and substances that this area of the body comes into contact with. For example, a rash around your ears, neck forehead or chest could indicate a reaction to a shampoo, conditioner or hair moisturiser. Monitor yourself. Stay very attentive to the substances you are exposing to that area of the body. Write them down as you become aware of them and reframe from coming into contact with them for up to 30 days to test your body's reaction.
Ask your doctor about performing a blood or skin test as a diagnostic tool.
Consult with your doctor before beginning your elimination diet.