To continue with the theme of itching and scaling scalps, yes you can develop allergies to your shampoo and other hair products. This is called allergic contact dermatitis. Things to look for are dry scaly patches, itching, redness, pus bumps, weeping and oozing on the scalp within 24-48 hours after using a product. If you are experiencing these symptoms after you wash your hair or perform any other chemical process, there is a chance you may be allergic to a substance in the product.
The best way to identify the culprit product is to take a product vacation. Copious rinsing will help remove any excess chemical residue left on the scalp and hair. If your symptoms do not resolve and are persistent or painful seek medical attention. After the symptoms resolve (and if they were mild), add each one of your hair products back into your regimen on a weekly schedule. For example, first add your shampoo, then wait a week and add your conditioner, and follow suit with each styling product. I call this the slow restart method. You may have to find alternative ways to style your hair without the use of your normal regimen of products during this time.
If the symptoms recur after re-entry of a product (the symptoms will return usually within 24-48 hours), try substituting that product for a hypoallergenic (no fragrances or dyes) one. There are many hypoallergenic brands that make hair products as listed below but be cautious manufacturers constantly change their product formulations. The basics include shampoos, conditioners, and styling products that are functional but may not have all the bells and whistles such as a luxurious lather, all day hold, and fragrances. You can also try natural products but again be cautious because some natural ingredients may cause allergic reactions as well. Some common hair product allergens and alternatives to those products are listed below:
As a dermatologist, I frequently see allergic contact dermatitis. Any obvious culprit products or those discovered with the slow restart method are eliminated and product substitutions are made. If a reaction recurs despite substitutions, there may be a chance that the patient has an allergy to a substance common to several hair products. At this time we discuss performing a patch test. The patch test entails placing strips of paper tape containing 25 to150 of the most common allergens in products (unlike the pinprick allergy test which tests for food and environmental allergens) in your back. The patch test strips are left on for 48 hours and the back is evaluated for a reaction at 2 days, then again at 5 days and for certain chemicals, at 10 days. For more information on patch testing, visit http://dermnetnz.org/dermatitis/standard-patch.html. If there is a positive test the patient then brings in their products and we sit and read and eliminate any products containing the allergens that were positive on the patch test. I also caution while patch testing can be helpful, it can be misleading at times and may not always reveal an answer.
A common misunderstanding is that you cannot become allergic to a product you’ve used for years. You most certainly can. Every product should be subjected to the slow restart method. So remember, product vacation, then slow restart method to see if you can find the culprit. If you identify the product causing the symptoms, replace it with a similar hypoallergenic product and hopefully the problem will resolve.