"Hypo" means "under" or "less than," so "hypoallergenic" means a product is less likely to trigger an allergic reaction.
Many products that we use every day, such as cleansers and soaps, deodorants, makeup, and even mouthwash, have ingredients that can irritate the skin or act as antigens (substances that act as an allergy trigger). Exposure of the skin to these ingredients -- most often fragrances and chemicals used as preservatives -- can lead to a condition called contact dermatitis. Contact dermatitis appears as areas of redness, itching, and swelling on the skin, and sometimes as a rash or blisters.
Many manufacturers of cosmetics and cleaning supplies now market their products as "hypoallergenic," meaning the products do not contain ingredients that are known to cause irritation or allergic reactions. However, manufacturers are not required to prove the claim that their products are hypoallergenic, and there are currently no regulations or standards for manufacturers to follow.
Although choosing products that are hypoallergenic may help reduce the risk of contact dermatitis, no product can guarantee never to irritate the skin or produce an allergic reaction. It's always a good idea to test any new product before you use it, especially if you have had skin reactions in the past. To test it, simply put a sample of the product on your inner wrist or elbow and wait 24 hours to see if a reaction occurs.