The cause of sensitive skin is on the inside - in your genes. Your skin is inherently sensitive. Truly sensitive skin is a genetic condition - you will have been born with sensitive skin, maybe with a lower amount of pigment, a thin epidermis, and blood vessels close to the skin surface, which is what causes a redness in appearance. Your epidermal lipid barrier, the outer layer of your skin that does the protecting job we talked about earlier, will have a defect and so will allow allergens and chemicals in, irritating the skin.
Sensitised Skin is what most of us who say we have sensitive skin actually have, and if the cause of sensitive skin is on the inside, then the cause of sensitised skin is on the outside - the result of lifestyle, environment and products. Sensitised skin reacts to changes in lifestyle - stress, lack of sleep; the environment - pollutants, cigarette smoke, weather conditions such as sun exposure; and the use of certain products - some fragrances, essential oils and natural products can cause a reaction.