We get a lot of foam when we rub shampoo into our hair, but no foam is formed if the same shampoo is rubbed on the skin. Why?
Foam or lather is a collection of tiny soap bubbles formed by trapping air. Foam or lather cannot form if air is not forced into the soapy solution. There is a lot of air trapped in the hair and when the shampoo is rubbed into it, the air forms bubbles in the solution, and we see this collection of bubbles as foam. You cannot get foam on a bald head, for example.
The skin is exposed to air, but not much air can be forced into shampoo spread on the skin merely through the action of rubbing.
In the process of shaving too, lather is formed by working air into the shaving cream with the help of the shaving brush.
Picture Credit : Google
