When people get a reaction, the first thing most think is, “OMG I have an allergy!” A good general rule of thumb is: if it burns, it's indicative of an irritation, while itching is usually a sign that you're having an allergic reaction.
If you're trying something new, it might be a particular ingredient or compound that's causing the issue, it might be too strong for you. Dry air can also cause your skin to become dry and itchy, when we add a new product to the combination, it can also trigger a reaction.
If the product has expired, it may not hold the ingredients in the same way, which may cause a reaction. In other words, once the chemical bonds of a product break down, the ingredients aren't suspended in the same way which means something you've used for years can suddenly turn on you. Always check for the expiration date on products. If your product is older than twelve months, it's probably time to get rid of it.
Be mindful of where you keep your products. Constant change in temperature can also affect the ingredients.
If you’re having a reaction or discomfort stop using it, stop using everything. You don’t want to start applying other products on top and making homemade soothing potions and lotions. The goal is to reduce the inflammation. For some that maybe using 1% hydrocortisone, some may also take Advil or Benadryl.
If it's itching, then it’s a little more serious. You can always go see your dermatologist and have them diagnose if it’s a true allergy or just an irritation.