Allantoin is a naturally occurring chemical compound that helps moisturize and smooth skin. Your own body makes allantoin. It's also derived from plants like comfrey.

Human bodies make allantoin, especially during exercise. And it's found in some plants as well.

And unlike some other ingredients that you need to seek out, allantoin is already built-in to a long list of skin care and beauty products.

That includes things like:

Moisturizers for your face, hands and body; Facial cleansers; Acne care products; Serums; Eye cream and eye masks; Face masks; Toners; Lipstick; Lip balm and chapstick; Mascara; Shampoo, conditioner and hairspray; Body wash; Oral care products, like toothpaste and mouthwash;Ointments for cuts, burns and wounds; Diaper cream; Shaving cream and aftershave

Benefits are antioxidant, anti-inflammatory and moisturizing properties. Allantoin can tone down the dryness of the individual cells.  It increases the water content of the skin, which means it helps to hydrate and moisturize.*

References
* Cleveland Clinic