Embryology · Skeleton, muscles, limbs and skin

Skin, hair, nails and the mammary glands !

Embryonic structure

The outer layer of skin, hair, nails and glands come from ectoderm; the deep layer from mesoderm; the colour from the neural crest.

Updated 2026-11-01

See it in 3D: Skin · Nipple · Mammary gland lobes · Areola · Breast fat

What it is

Skin has a dual origin: the epidermis comes from surface ectoderm and the dermis from the underlying mesenchyme. Melanocytes arrive from the neural crest in the first months. Hair, sebaceous, sweat and mammary glands are epidermal buds that grow down into the dermis. The mammary line explains extra nipples.

Key facts

Start of the second month: the single ectodermal layer lays down a periderm on top.
End of the fourth month: the epidermis has its four layers (basal, spinous, granular and horny).
First 3 months: neural crest melanocytes invade the epidermis.
Dermis: lateral plate mesoderm (limbs and body wall), somite dermatomes (back) and neural crest (face and neck).
End of the third month: the first hairs appear on the eyebrows and upper lip; by about week 20 the fetus is covered in lanugo.
Nails: nail fields appear at the fingertips at the end of the third month and reach the tips around the ninth month.
Week 7: the mammary line runs from axilla to groin; only the thoracic segment persists.

Structure

Basal (germinative) layer: makes new cells; its ridges leave the fingerprints.
Vernix caseosa: sebaceous secretion with epidermal cells and hair; protects the skin from amniotic fluid.
Hair follicle: an epidermal bud with a mesenchymal papilla; the arrector pili muscle is mesodermal.
Mammary gland: 16 to 24 epidermal sprouts that canalise into lactiferous ducts; at birth the nipple is a pit that later everts.

What it becomes

Epidermis: barrier, keratin and fingerprints.
Dermis: support, vessels, nerve endings and deep fat.
Eccrine sweat glands: thermoregulation; apocrine glands open into hair follicles (axilla, pubis).
Mammary gland: no alveoli at birth; pubertal oestrogen and progesterone form them.

Markers

EDA
EDAR
PAX3
SOX10
KIT
MITF

Clinical notes

Polythelia: extra nipples along the mammary line, mostly in the axilla and chest.
Inverted nipple: the ducts open into the original pit, which fails to evert.
Hypohidrotic ectodermal dysplasia (EDA): sparse hair, few teeth and very little sweat.
Waardenburg (PAX3 and others): white forelock, different-coloured eyes and hearing loss, from melanocyte failure.
Ichthyosis: excess keratinisation; the harlequin form is the most severe.

Test yourself

Think of the answer, then tap the question to see it.

Which germ-layer population gives rise to melanocytes?

The neural crest; they migrate into the epidermis during the first three months.

What explains extra nipples in the axilla or on the abdomen?

Persistence of fragments of the mammary line, which in week 7 runs from the base of the arm to the base of the leg.

What is vernix caseosa?

A whitish coat of sebaceous secretion, epidermal cells and hair that protects fetal skin from amniotic fluid.

Where does the dermis of the face come from?

From neural crest; trunk dermis comes from lateral plate mesoderm and the somite dermatomes.

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The structures of Durgical's 3D anatomy where it is found.

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Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Hypohidrotic ectodermal dysplasia: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Waardenburg syndrome: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Langman's Medical Embryology, 13th ed., ch. 21: Integumentary System (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.