In primary milia cases, like the miniscule cysts that appear on a newborn, the skin just can't remove the dead skin cells. That means, instead of being sloughed of, the cells get trapped and clog oil-producing pores [source: University of Maryland Medical Center]. This type of milia is really common in babies, but adults can get it, too.
Secondary milia occur when a skin condition that leads to blistering actually damages ducts in the skin. This also results in dead skin cells getting trapped when they try to crop up to the surface, and when enough dead cells are present, the tiny dome-shaped bumps you see in primary milia stage a surprise visit. Burns or rashes like poison ivy can cause enough blistering to increase trapped skin cells on the surface. But skin diseases such as bullous pemphigoid, which causes chronic blistering, can also lead to secondary milia [source: Skin Sight].
In some adults, sun damage is also a major contributor to milia, because it thickens and toughens the outer layers of skin, making it harder for dead skin cells to find their way out of glands. The cysts then form in the areas that were overexposed to unforgiving rays. Other causes of milia include topical steroid use or spa treatments such as skin resurfacing procedures or dermabrasion [source: Skin Sight].
As with skin procedures that cause trauma and affect skin's exfoliation, anything you put on your face or in your hair can add oil to your skin and affect your pores. For example, heavy, creamy skin care products that are comedogenic, or pore clogging, can also contribute to the occurrence of milia.
If you're interested in tackling your milia outbreak at home, read on to learn about some steps you can take.