When used according to the label directions, spot-on products are well tolerated by most pets. However, as with any product that is applied directly on the skin, there is the possibility that certain individuals will have adverse local reactions to one or more ingredients in the product. Some individuals will have similar reactions to many different spot-on products with different active ingredients, suggesting that their sensitivities may be to some of the inactive ingredients. These reactions are restricted to the area of skin that comes in direct contact with the product, so they do not reflect a systemic toxicosis but rather a local hypersensitivity. Skin reactions to spot-on products can vary from mild tingling sensations to actual chemical burns of the skin in especially sensitive individuals.