When we touch a window or a mirror, we leave a print. It is due to a fat called the sebum which soaks our epidermis and our skin. The sebum has a very important role; it is in particular a nutritive and softening factor for the skin. The skin of the dog and the cat is also covered with sebum. It is this sebum which will transport the active ingredient. Indeed, the molecules used in the collars are very soluble in the sebum. They will diffuse via this fatty layer on the whole surface of the body. Thus, a flea collar carried around the neck protects the animal completely, from the head to the tip of the tail.