You may occasionally find that you experience a sudden allergic reaction, even with cosmetics that you’ve used before without incident. Certain people may experience inflammations, including rashes or swelling, even if others do not. This is known as having an “allergic constitution”. With cosmetics and metals for example, antibodies can be formed through repeated contact with the skin. This may lead eventually to dermatitis. Allergic reactions happen only in a few people, but when they do appear they tend to do so suddenly. Once an allergic reaction does happen, that person may continue to be allergic to that particular substance for life. Should you experience any symptoms when using cosmetics, stop using the product immediately (even if it is a product for sensitive skin). See a dermatologist for medical treatment as soon as possible.