These tiny cysts are filled with keratin - the protein found in skin, hair and nails - when, instead of being eliminated, these clusters of dead skin roll up to form a ball under the surface of the skin forming these tiny bumps. And they really are tiny, usually no bigger than 1-2 millimetres in diameter.
Although we do not yet know everything about the cause of these white bumps, there are aggravating factors. Milia is sometimes linked to sun exposure or repeated steroid cream use, but it is also genetic, meaning some people are more prone to them than others. But they can affect all skin types - dry, combination, sensitive or oily - and all ages, from baby skin to mature skin.