This is all going to depend on the active ingredients within the formula so read the instructions closely. Some people will find ingredients like menthol and peppermint irritating the skin. You may find that you become itchy, experience pain or swelling of the skin. If this does happen, just wash it off thoroughly and stop using the product. It’s important to read the ingredients list thoroughly to ensure you are not allergic to anything. There are also potential side effects involved with the use of vasodilators. Most people can use these with no issue but they can create feelings of dizziness, headaches, or increased heart rate. As a basic rule, avoid these products if you are taking any prescription drug, have heart disease, high blood pressure, or are taking an MAO inhibitor. Also, avoid these products if your partner is pregnant. Remember that these products are not going to give you permanent gains (sorry guys!) But, they can help to increase blood flow, prolong your play before ejaculation and create a fuller looking and feeling penis for more fun and confidence while you play. If you have any concerns with these products, please contact your doctor, better safe than sorry.