Introduction

Milia are tiny, pearly white bumps that can appear on the skin, usually measuring about 1–2 mm in size. These small, superficial cysts are filled with keratin and although uncommon, may appear in large clusters. Milia may be present at birth or can be caused by various skin conditions that cause blistering or damage to the skin. Around 50% of full-term babies may develop these little lumps, which are usually harmless and typically resolve on their own within the first months of life, leaving no scars.  However, self-removal may lead to brushing, scarring and infection in adults. Dermatological treatment should be sought to avoid such complications.

Classification of milia

Primary milia are the most common form, resulting from trapped keratin beneath the skin. They can occur at any age, including infants. These little, white or yellowish lumps are typically found on the face, particularly near the eyes and cheeks, where they occur in the lower part of small hair follicles.

Primary milia may also be associated with certain genetic skin diseases. One rare variety, milia en plaque, appears as microscopic cysts on a red patch of skin, but the specific causes are unknown.

Congenital Milia occurs at birth and impacts approximately 40% to 50% of babies. They are commonly found on the nose, scalp, upper trunk, and extremities. These milia usually dissolve on their own within a few weeks or months.

Secondary Milia appear after the skin has been damaged by trauma, burns or rashes. It may occur secondary to skin conditions such as acne, epidermolysis bullosa, bullous pemphigoid, bullous lichen planus, and porphyria cutanea tarda, or certain skin procedures such as dermabrasion or radiation treatment. It can also be caused by overuse of steroid creams. They resemble basic milia but develop at the location of a skin injury or disease, usually on the top layer of skin, or in sweat ducts or oil ducts. While secondary milia may go away on their own, they tend to persist longer than primary milia.⁴

Genodermatosis-associated milia are linked to certain genetic skin disorders and can appear anywhere on the body, depending on the associated condition. These milia are part of the broader symptoms of the underlying genetic disorder.^3,4

Causes of milia

Milia are benign (non-cancerous) cysts that develop inside the cutaneous epithelial system, which includes the epidermis (the outermost layer of skin), hair follicles and oil glands. These cysts are designed particularly to produce keratin. Milia can develop spontaneously in predisposed individuals with no known cause (primary milia) or be induced by a variety of factors that significantly disturb the skin, such as dermabrasion, skin grafts, physical trauma (including x-rays), congenital ectodermal defects, and inflammatory skin conditions such as acne (secondary milia). The exact cause of milia versus other types of tumours is unknown. 

Milia can arise from a wide range of epithelial tissues, but their location depends on the underlying cause. On the face, milia commonly arise from the external root sheath of vellus hair follicles (also known as peach fuzz). However, in other types of secondary milia, more research is needed to identify a specific point of origin.

Treatment of milia 

Milia in babies commonly resolves itself within the first few months without treatment.  In adults, milia can persist for a long time, but sometimes they can resolve on their own. Even though milia appear on the skin's surface, they are hard to remove without proper tools. It's important not to attempt to remove them at home because you might end up causing scarring. If milia are bothersome, it's best to consult a dermatologist.⁶ There are several cosmetic methods available, including removing them with special instruments or laser treatments. The choice of treatment depends on the number of milia and how they impact the individual.¹

Complications of milia 

While milia are normally harmless, milia can persist and reoccur, causing cosmetic issues such as scarring. Picking or squeezing milia may lead to scarring, bruising or infection, so it is important to avoid this.  Consulting a dermatologist can help you find the right treatment.²

Milia may also complicate the diagnosis ofco-occuring skin disorders such as epidermolysis bullosa and bullous pemphigoid, where the skin has been blistered or traumatised. This can prevent timely diagnosis and treatment. Having milia may have an impact on how someone perceives themselves, particularly when dealing with other skin issues, which can affect an individual’s self-esteem. However, milia does not lead to wider systemic issues in the body. 

Potential risk factors 

• Blistering Skin Conditions: Conditions that cause blister formation may cause  milia as the skin heals from these blisters
• Sun Damage: Long-term exposure to sunlight without protection can cause permanent damage to the skin, disrupting the natural exfoliation process of the skin, which can potentially lead to the formation of milia
• Topical Steroid Creams: Prolonged use can alter the skin's structure and function, interfering with the ability to exfoliate properly.
• Skin Resurfacing Techniques: Procedures like dermabrasion or laser resurfacing are used to improve skin texture and appearance. However, these techniques can sometimes disrupt the skin's natural processes, causing milia to form.
• Ageing: As people age, the skin's ability to shed dead cells and renew itself decreases, leading to a buildup of dead skin cells and keratin, contributing to the development of milia
• Autoimmune Disorders: Conditions where the immune system attacks healthy tissues can lead to skin issues, including milia
• Poor Skin Care: Not following a proper skincare routine can contribute to skin problems, including milia
• Cosmetics: makeup or skincare products that clog pores can also be a factor
• Sleep Habits: Inadequate sleep can affect overall skin health and potentially contribute to milia
• Skin Conditions: Having conditions like eczema, rosacea, or dandruff can predispose individuals to skin issues, including milia⁷ 

Summary

Milia are small, harmless cysts that form when sweat glands or hair follicles regenerate.  They can arise spontaneously or result from skin damage due to burns, rashes, or certain medical treatments. There are several types of milia: primary milia form from trapped keratin under the skin, congenital milia present at birth on newborns, secondary milia developing after skin trauma or procedures, and those associated with genetic skin disorders. While generally harmless, milia can persist and cause cosmetic concerns. Attempting to remove them at home is not recommended due to the risk of scarring; consulting a dermatologist for safe removal options is advisable. Understanding the underlying cause is crucial for proper diagnosis and management, ensuring effective treatment and minimising complications.