Introduction

Have you ever spotted white bumps on your skin that look like acne but are practically impossible to pop? These bumps are called milia. They are small cysts that form when dead skin cells are trapped beneath the skin's surface. While harmless, milia can make the skin look grainy and unpleasant to touch. The good news is that in most cases, milia can be prevented with proper skin care and a healthy lifestyle. In this article, we will look into the biology of how milia develops, as well as prevention strategies for milia.¹

What is milia?

Milia (singular: milium) are tiny white bumps on the skin, most commonly on the face. They are widely known as milk spots and can be found in all age groups but are notably common in healthy newborns with a prevalence of about 50%. Milia are practically harmless and often even go away without scarring. 

Milia is often confused with acne. Acne results from clogged skin pores with sebum and dead skin cells, leading to bacterial infection and inflammation. Acne lesions are usually red and tender to the touch and may be filled with pus or tissue fluid. While milia can be caused by acne, they often result from clogged sweat glands or other subepidermal structures. Also, unlike most acne lesions, milia are cysts and usually cannot be popped by hand, and need to be extracted with an incision by a specialist.¹

What causes milia?

Milia form whenever keratin is trapped under the epidermis - in skin pores, sweat glands or other skin structures. Keratin is then encapsulated, and a cyst is formed. Milia are usually very hard to extract by hand due to the hard shell covering the keratin plug. Since milia formation is related to how skin cells, understanding your skin is important.¹

Skin healing

When skin is injured, it begins to heal and strives to return to its typical condition. The healing process in the skin as a reaction to injury can influence the rate of skin cell turnover. Skin repair entails several processes such as inflammation, skin cell proliferation, and subsequent differentiation, which can disrupt skin peeling and result in milia. This disruption results in the trapping of keratin. The excess keratin becomes enclosed in a small sac that is rich in collagen and calcium, leading to the development of cysts.²

Factors causing the formation of milia

Milia generally occurs when the normal process of skin healing and regeneration is disrupted, leading to the trapping of keratin and the formation of cysts under the skin's surface.² Milia can also develop whenever there is damage to the epidermis. Some common causes include:

• Physical damage: mechanical injuries, burns, and rashes can affect normal skin cell differentiation and shedding, leading to keratin trapping and the formation of milia¹
• Sun damage: Skin cells divide more frequently in response to prolonged exposure to UV light, forming a protective barrier. This leads to skin thickening and can impair the shedding of mature skin cells, causing the formation of milia³
• Genetics: apart from being a skin condition on its own, in some cases, milia can be a symptom of an underlying inherited condition, like the following:
  • Bazex–Dupré–Christol syndrome: a rare X-linked recessive disorder⁴
  • Oral-facial-digital syndrome type 1: a rare X-linked recessive disorder caused by mutations in the OFD1 gene⁵
  • Marie-Unna hereditary hypotrichosis: a rare autosomal dominant disorder caused by mutations in the U2HR gene⁶

• Medication: Long-term use of topical corticosteroids can lead to the formation of milia. In such patients, milia are usually accompanied by telangiectasia (dilated capillaries) and signs of skin atrophy (fine wrinkles)⁷
• Autoimmunity: Milia are a common feature of some autoimmune skin conditions associated with skin blistering, including pemphigus vulgaris and bullous pemphigoid^8,9
• Infancy: As mentioned above, milia are very common in infants. This is caused by the immaturity of their skin, as keratinocytes of newborns are not able to differentiate and shed off properly¹

Prevention strategies

Proper skincare routine

A proper skincare routine is the best way to prevent the formation of milia. The minimum of skincare includes using a cleanser, moisturiser, and sunscreen.

Cleansers

Cleansing with a gentle, non-comedogenic cleanser is important to keep skin pores clean and prevent the retention of keratin plugs in the epidermis. People should use cleansers appropriate for their specific skin type. The use of aggressive cleansers not suitable for your skin can irritate and disrupt normal skin regeneration causing milia.¹⁰

Moisturisers

When dead keratinocytes reach the skin surface, enzymes in our skin help separate them from neighbouring cells, proceeding to shed off. These enzymes need to be surrounded by an adequate amount of water to function properly. When the skin is dry, shedding does not happen properly and keratinocytes stack on top of the skin, making it look flaky. The buildup of keratinocytes in the epidermis can lead to milia hence, moisturising is crucial for preventing their formation.¹¹

Sunscreen

Sunlight can cause skin thickening and milia outbreaks. Sunscreen with a high enough sun protection factor (SPF) can provide protection of the skin cells from UV light and prevent milia. Different types of sunscreen protect the underlying skin from UV light penetration but in different ways. 

Inorganic sunscreens (also known as physical and mineral sunscreens) use different minerals such as zinc oxide and titanium dioxide, which reflect light. On the other hand, organic sunscreens (also known as chemical sunscreens) use chemical compounds like oxybenzone and avobenzone, which absorb UV light. Some products combine both types of sunscreens to maximise their SPF.¹²

Exfoliants

In milia-prone skin, the addition of an exfoliant can help in the formation of these persistent cysts. Exfoliants help skin cells shed off more easily and prevent keratin trapping. Exfoliants can be divided into two groups: mechanical and chemical. Mechanical exfoliants use abrasive particles to strip off parts of the outermost epidermal layer. Examples include sponges, crushed nuts, and salt. Mechanical exfoliants are generally not recommended over chemical ones due to them causing microscopic tears in the skin, potentially interfering with normal skin healing. 

Chemical exfoliants help loosen up and break down the bonds holding the keratinocytes. Examples include alpha hydroxy acids (AHAs) like glycolic and lactic acid, beta hydroxy acids (BHAs) like salicylic acid, and vitamin C (ascorbic acid). AHAs and vitamin C are more water soluble and can have a harder time getting through the lipid-rich structure of the epidermis, while salicylic acid not only is more lipid-soluble and more effective in exfoliating dead skin cells but also has anti-inflammatory properties and can help balance off inflammatory processes in skin healing. The improper use of exfoliants can lead to a damaged skin barrier, causing sensitivity and inflammation in the skin. ¹³

Retinoids

Topical retinoids such as retinol and retinal creams can also be beneficial for the prevention of milia. Retinoids interact with retinoid receptors that are plentiful in skin cells. Upon activation, these receptors influence protein production within skin cells, resulting in a more youthful appearance by diminishing wrinkles and age spots while enhancing the skin's overall texture. 

Retinoids stimulate skin cell differentiation making it easier for dead keratinocytes to shed off, thus preventing the formation of milia. The improper use of retinoids can cause skin irritation, flaking, and photosensitivity, so they should be used cautiously until the desired effect is reached.^14,15

Healthy lifestyle changes

A healthy diet

The skin is the largest organ of the human body and needs a constant supply of nutrients and water to maintain its structure and functions. Such nutrients include:^16,17

• Amino acids: The skin uses amino acids from food sources as building blocks for collagen, which is important for the healthy structure and appearance of the skin, as well as vitamins and minerals that serve as cofactors for collagen synthesis
• Antioxidants: consuming fruits and vegetables rich in vitamins and other antioxidants can protect skin cells from free radicals and maintain normal skin cell turnover
• Omega-3 fatty acids: are important for maintaining a healthy lipid barrier of the skin, preventing excess water loss and keeping the skin moisturised. Flaxseed and fatty fish are great sources of omega-3 fatty acids
• Drinking water: drinking adequate amounts of water is important to keep skin elasticity and moisture, which are both essential for overall skin appearance and normal skin shedding

Physical activity

Regular physical activity benefits the skin by increasing blood flow to the skin, which delivers oxygen and nutrients to skin cells and enhances normal skin cell turnover. Sweat and adequate skin hygiene can help unclog skin pores and prevent the accumulation of sebum and dead skin cells. Sweating can also provide hydration and nutrients to skin cells, acting as an efficient skin moisturiser.¹⁸

Summary

Milia are small white bumps usually found on the face and can occur in people of all ages, especially healthy newborns. It occurs when dead skin cells get trapped beneath the skin's surface. Although harmless, milia can make the skin look uneven and feel rough. Fortunately, milia can often be avoided through proper skin care and a healthy lifestyle. They are frequently confused with acne however, milia are cysts and usually need medical extraction rather than being popped by hand. Physical damage, sun exposure, genetics, long-term use of corticosteroids, and certain autoimmune conditions can contribute to milia formation. Infants often have milia because their skin cells are not fully developed. To prevent milia, maintaining a proper skincare routine is essential. This includes using a gentle cleanser, a good moisturiser, and sunscreen. Exfoliants can help remove dead skin cells, while retinoids can promote skin cell turnover. Eating a balanced diet with essential nutrients and staying hydrated support healthy skin. Regular physical activity also boosts blood flow and helps keep skin clear by preventing clogged pores.