What causes pimples on a baby's scalp?

Causes of Pimples on a Baby's Scalp

Pimples on a baby's scalp are most commonly caused by neonatal acne, seborrheic dermatitis (cradle cap), or neonatal cephalic pustulosis, all of which are benign, self-limiting conditions triggered by hormonal influences, yeast colonization, or sebaceous gland activity.

Primary Causes

Neonatal Acne

• Occurs in approximately 20% of newborns between the second and fourth weeks of life, presenting as open and closed comedones that can evolve into papules, erythematous pustules, and rarely nodules 1
• More common in males (4.5:1 male-to-female ratio) and affects the forehead, cheeks, chin, and eyelids, but can spread to the scalp, neck, and trunk 1
• Caused by elevated placental and neonatal androgens (adrenal origin in both sexes, testicular in males) that enlarge sebaceous glands and increase sebum production 1
• Most cases are mild and self-limited, resolving spontaneously with gentle cleansing 2, 1

Neonatal Cephalic Pustulosis

• An acne variant caused by hypersensitivity to Malassezia furfur yeast, presenting as pustules on the face and scalp 2
• Typically self-limited, though severe cases may benefit from topical ketoconazole 2
• Distinguished from neonatal acne by its etiology (yeast hypersensitivity rather than hormonal) 2

Seborrheic Dermatitis (Cradle Cap)

• Presents as scaling on the scalp that can appear as greasy, yellowish scales or flakes 2, 3
• Benign and self-limiting, lasting from weeks to months, though it can distress parents 3
• Associated with Malassezia furfur and Staphylococcus aureus colonization in many cases 4
• Managed with shampooing and removing scales with a soft brush after applying mineral oil or petrolatum; severe cases may require tar or ketoconazole shampoo 2

Important Differential Diagnoses to Consider

Infectious Causes (Require Urgent Evaluation)

• Gonococcal scalp abscesses can result from fetal monitoring through scalp electrodes, presenting as localized pustular lesions 5
• Requires blood, CSF, and wound cultures on chocolate agar, with treatment consisting of ceftriaxone 25-50 mg/kg/day IV or IM for 7 days (10-14 days if meningitis documented) 5
• Congenital infections should be suspected in newborns with pustules or vesicles who are not well-appearing or have risk factors for congenital infection 6

Benign Transient Rashes

• Erythema toxicum neonatorum presents as erythematous macules, papules, and pustules on the face, trunk, and extremities, typically resolving within 1 week 2, 6
• Neonatal pustular melanosis is a transient pustular rash with characteristic appearance and distribution 6
• Milia can be differentiated from neonatal acne by their presence at birth, appearing as tiny white papules 2, 6

Clinical Approach

When to Reassure

• Isolated comedones, papules, or pustules on the scalp in a well-appearing infant aged 2-4 weeks suggest benign neonatal acne requiring only gentle cleansing 1
• Greasy scaling without pustules indicates seborrheic dermatitis managed with shampooing and scale removal 2

When to Investigate Further

• Severe or persistent acne beyond 1 year warrants evaluation for androgen excess (congenital adrenal hyperplasia or virilizing tumor) 2, 1
• Pustules in an ill-appearing infant or one with risk factors for infection require bacterial and viral cultures 6
• History of fetal scalp electrode placement necessitates consideration of gonococcal scalp abscess 5

Common Pitfalls

• Do not confuse neonatal acne (appears at 2-4 weeks) with milia (present at birth) 2, 6
• Do not overlook infectious causes in ill-appearing infants with pustules, as these require urgent systemic treatment 6
• Do not assume all scalp pustules are benign without considering the clinical context, particularly maternal STI history and use of fetal scalp electrodes 5