Milia are tiny white or yellowish bumps, usually no bigger than 3 mm, that form when a protein called keratin gets trapped just beneath the surface of the skin. They’re technically miniature cysts, not pimples, and they won’t pop like a whitehead because the trapped material sits under a sealed layer of skin rather than inside an open pore. Understanding what causes them depends on whether they developed on their own or after something happened to your skin.
How Keratin Gets Trapped
Your skin constantly produces keratin, a tough protein that forms the outer protective layer of your epidermis. Normally, dead skin cells containing keratin shed on their own. Milia form when that process gets disrupted and keratin accumulates in a tiny pocket beneath the skin’s surface.
Under a microscope, each milium looks like a miniature version of an epidermal cyst, with walls made of layered skin cells surrounding a core of trapped keratin. These cysts tend to originate from specific structures in the skin. In primary milia (the kind that show up without any obvious trigger), the cyst typically connects to the outer sheath of a fine vellus hair follicle, right near where the oil gland attaches. In secondary milia (the kind that follow skin damage), about 75% of cysts connect instead to sweat ducts, usually at a one-to-one ratio of one duct per milium.
Primary Milia: No Obvious Trigger
Primary milia appear spontaneously. They’re extremely common in newborns and frequently show up on the eyelids, forehead, cheeks, and sometimes the genital area in both children and adults. In babies, they typically resolve on their own within a few weeks as the skin matures and begins shedding normally. In adults, primary milia can persist indefinitely because the cyst wall is fully formed and the trapped keratin has nowhere to go.
There isn’t always a clear reason why primary milia develop in adults. Some people are simply more prone to them, and in rare cases the tendency runs in families. Researchers have documented families where multiple eruptive milia passed from father to son in a pattern consistent with autosomal dominant inheritance, meaning a single copy of the gene from one parent is enough to cause the condition.
Secondary Milia: Skin Damage and Trauma
Secondary milia form after something injures or disrupts the skin. When the skin heals, the normal architecture of pores, hair follicles, and sweat ducts can get rearranged or blocked, creating small pockets where keratin accumulates instead of shedding to the surface. Common triggers include:
- Burns, including sunburns severe enough to blister
- Blistering rashes from conditions like poison ivy or autoimmune blistering diseases
- Chronic sun damage, which thickens the outer layer of skin and impairs normal cell turnover
- Skin resurfacing procedures like dermabrasion, chemical peels, and laser treatments
Of these, dermabrasion carries the highest risk. Milia develop in up to 15% of patients after dermabrasion, compared to lower rates after chemical peels or laser resurfacing. The mechanism is straightforward: the procedure physically removes the top layers of skin, and as the skin rebuilds, severed oil glands and follicle remnants can form small cysts rather than reconnecting to the surface normally. Some of these structures initially lose their identity during healing and then re-form as milia instead of functioning glands.
Skincare Products That Contribute
Heavy, occlusive skincare products are one of the most common everyday causes of milia, particularly around the eyes. Thick eye creams, concealers, and oil-based makeup removers are designed to seal moisture into the skin, but that same barrier effect can trap keratin beneath the surface. The skin around the eyes is thinner than the rest of the face, making it especially vulnerable.
The issue isn’t any single ingredient but rather the overall heaviness and occlusiveness of the product. If you’re prone to milia, switching to lighter, non-comedogenic formulations around the eye area often helps prevent new ones from forming. This won’t resolve existing milia, since those are already sealed cysts, but it can stop the cycle of new ones appearing.
Topical Medications as a Cause
Certain prescription topical treatments can trigger milia as a side effect. Superpotent topical corticosteroids are a well-documented culprit. Prolonged use thins the skin and alters its normal turnover, creating conditions where keratin gets trapped more easily. This is especially relevant for people using strong steroid creams on the face for extended periods, where the skin is already thinner and more susceptible.
Milia en Plaque: A Rarer Pattern
Most milia appear as scattered individual bumps. In a much less common variant called milia en plaque, clusters of milia develop on top of an inflamed, slightly raised patch of skin, usually near the ears. This pattern is associated with underlying inflammatory conditions rather than simple keratin trapping, and it typically requires a skin biopsy to confirm the diagnosis and rule out other conditions that can look similar.
Why Milia Don’t Go Away on Their Own
Unlike a pimple, which eventually drains or gets reabsorbed, an adult milium is a fully enclosed cyst with its own wall of skin cells. There’s no opening to the surface, so the keratin inside has no natural exit route. This is why squeezing rarely works and can lead to irritation or scarring. The most effective removal involves a small nick in the skin surface to create an opening, allowing the tiny cyst to be extracted whole. Dermatologists typically do this with a sterile needle or small blade in a quick office visit.
For people who develop milia repeatedly, topical retinoids can help by accelerating skin cell turnover and preventing keratin from accumulating in the first place. Addressing the underlying cause, whether that’s a heavy moisturizer, chronic sun exposure, or a medication side effect, is the most reliable way to keep them from coming back.