You should always patch test a new skin care product—no matter what patch testing is important because there are a number of allergens in products that can cause an itchy rash. You may experience an adverse reaction to a product simply because your skin doesn’t like a specific ingredient (natural or otherwise), or it doesn’t respond well to the way a product is formulated. This can cause your skin to dry out, increase oil production, or prompt an angry breakout. Note that that some ingredients are more likely to cause a reaction than others. If you have acne-prone skin, ingredients to look out for should include coconut oil and butter, cocoa butter, lanolin, and isopropyl palmitate. A really awful reaction will be quite noticeable. Your skin will likely look red, bumpy or splotchy, and it will feel itchy or painful. In this case, you should absolutely discontinue use and either toss the product out or hand it off to a friend who may have better fortune. You can treat the area with a soothing product, such as aloe vera or milk of magnesia.