1) The skin develops from surface ectoderm and underlying mesoderm. Key stages include specification, morphogenesis, and differentiation as the epidermis stratifies and cornification occurs. 2) Specialized cells like melanocytes and Langerhans cells arise and mature according to defined timelines. Dermal components also develop from distinct embryonic origins. 3) Skin appendages form through epithelial-mesenchymal interactions, with hair follicles, sebaceous glands, nails, and sweat glands developing in parallel through gestation. The dermal-epidermal junction also acquires mature structures by 12 weeks.

1. Development of skin……
Dr. Amy Mary Sebastian

2. Development of
•Epidermis
•Specialized cells within epidermis
•Dermis & hypodermis
•Dermal epidermal junction
•Skin appendages
Skin stem cells

6. Embryonic origin of skin
•Ectoderm Keratinocytes,Merkel cells
Melanocytes,Neurones
•Mesodermal Fibroblasts,Langerhans
cell,Endothelial cell,
Hematopoietic cells

7. 3 Stages of fetal skin development:
•Specification-0-60 days
•Morphogenesis – 2 to 5 months
•Differentiation- 5 to 9 months
SpM Dept

9. • Single layered surface ectoderm
• Basal layer
• Periderm + Basal layer
• Periderm + Intermediate layer + Basal layer- 8 wk
• Epidermal stratification
• Cornification-22-24 wks
• Periderm sloughs off-24-26wks

10. Clinical relevance
• Collodion baby
• Defect in
Transglutaminase1
• Lipid processing
enzymes- ALOX3,ALOX12
• Lipid transporter- ABCA12

11. Harlequin Ichtyosis: ABCA 12 gene
Defective lipid transport into lamellar bodies

12. Development of specialized cells within
epidermis
1.Melanocyte 2.Langerhans cell 3.Merkels cell
1st seen @ 50 days @40 days @8-12 wks
Dendritic morphology Dendritic morphology C.dense core granules
HMB45 Ab +ve r/n CD45,HLA DR,CD1c Cytokeratin 20
ATPase activity Neuropeptides
From neural crest Mesoderm cells Ectoderm

13. Melanocytes
•Derived from neural crest
•Migrate dorsolaterally and ventrally
•Also from schwann cell
precursor
•Becomes functional 3-4m
•Melanosome transfer- 5m
•Density towards birth

14. Active melanocytes in dermis during embryonic period
Migrate to epiderms / Apoptosis
Disappears by birth, may persist in
some areas(Presacral, dorsum of distal
extremities,head and neck)
Mongolian spots

15. Langerhans cell
• Density low in early gestation increases during 3rd
trimester.
Merkel cell
• Highly innervated neuroendocrine cells
• Involved in mechanoception.
• Found in basal layers of epidermis associated with
appendages & nerves.

16. Clinical relevance:
Waardenberg syndrome
• Due to failure of melanocyte
precursors.
• Causative genes
MITF,PAX3,SOX10,SNA12
• Also membrane receptors & ligands-
Endothelin 3,Endothelin B,KIT

17. Development of dermis & hypodermis.
• Neural crest- face & frontal scalp
• Paraxial mesoderm-somite-dermomyotome- dermis of
back
• Lateral plate mesoderm- dermis
of extremities & central trunk
• 6-8 wks –dermal fibroblasts
secrete collagen III & I (3:1)

18. • 9 wks-demarcation b/n dermis & subcutis
• 12 wks-demarcation b/n papillary & reticular
dermis, collagen assemble into fibers
• End of 2nd trimester-dermis shifts from scaring to non
scarring type
• Dermal vasculature-starts at13 wks,matures fully at
birth. Regulated by VEGF,Tie 1&2,Ang 1&2
• Dermal nerves-follows vascular pattern
• Hypodermis-starts during 2nd trimester,continues in 3rd

19. Clinical relevance
• EDS-dermal structural proteins are
defective
• Cutis laxa with severe pulmonary,GIT &
Genitourinary malformation-LTBP4
• Goltz syndrome-focal dermal hypoplasia
PORCN gene, effector of Wnt signalling pathway
Goltz syndrome

20. Development of dermo-epidermal junction
• Flat embryonic DE junction-L. densa & L. lucida
composed of molecules common to all BM.
• 8wks-skin specific components
• 12wks-structures of mature DEJ-
hemidesmosomes,anchoring filaments,BPAG etc.
• Finally acquires rete ridges & dermal papillae like
adult DEJ.

21. Development of skin appendages
• Epidermal & dermal components
• Signals sent back & forth b/n epidermis & dermis.
Hair follicle development
• Epidermal placodes (10-11 wks)
• Presumptive dermal papillae
• Hair germ (12-14 wks)
• Hair peg

23. Hair follicle development

24. During 2nd trimester –
7 concentric layers
• 18-21 wks hair canal formed
• 24-28wks-1st wave of
shedding.
• Next hair cycle begins
• Perinatally-2nd wave of shedding.
• Hair cycle continues throughout life, but becomes
asynchronous after birth.
• SHH-Sonic hedgehog,HOX 13,FOX N1

25. Sebaceous gland development
• Parallels hair follicle development
• 13-16 wks-superficial bulge
• 2nd & 3rd trimester-Maternal hormones cause gland
hypertrophy.

26. Nail development:

27. • 8-10 wks-folds visible at dorsal digital tips
• 13wks-proximal nail folds
• Ventral to nail fold nail matrix cells produce nail
plate
• Preliminary nail is shed-hard nail plate 4th mth
• Nail completely covers nail bed 5th mth

28. Eccrine & apocrine sweat gland development.
• Palmplantar eccrine –large mesenchymal pads
(55-65 days)
• Parallel ectodermal ridges overlying the pads
• At regular intervals, individual eccrine gland primordia buds
along the ridges.
• Buds elongate as cords-enter M.pads
• 16 wks-glandular structures & dermal duct canalization
• 22wks-epidermal duct canalization

29. Development of sweat glands

30. Interfollicular eccrine glands
• Arise independently -5th mth
• Do not function in utero
• Begin functioning post nataly
Apocrine glands
• Upper portion of hair follicle-5th mth
• Clear cells & dark cells(mucin secreating)-7th mth
• Quiscent in neonates, starts functioning during puberty

31. Clinical relevance
• Hypohydrotic ectodermal dysplasia(HED)-
Ectodysplasin A
• Also from genes involved in epidermal development.
• Ankyloblepharon ectodermal dysplasia cleft lip/palate
(AEC)-P63
• Ectrodactyly ectodermal dysplasia(EEC)-P63

32. Ankyloblepharon ectodermal dysplasia cleft
lip/palate (AEC)-P63

33. Ectrodactyly ectodermal dysplasia(EEC)-P63

34. Skin Stem cells

35. In a nutshell….
• Surface ectoderm gives rise to keratinocytes
& merkel cells,while Neurectoderm –
melanocytes & dermis of face & frontal scalp.
• Development of skin is conceptually divided into
specification , morphogenesis & differentiation.
• Basal cells of epidermis gives rise to periderm f/b
intermediate layer , finally epidermal stratification &
cornification leading onto sloughing of periderm.

36. In a
nutshell..
• Langerhans cells precursors are seen from 40 days, while
merkel cells are detected at 8-12 wks.
• Dermis of face & frontal scalp develop from neural crest,
while paraxial mesoderm gives rise to dermis of back,
whereas dermis of ventral trunk & extremities are from
lateral plate mesoderm.
• Melanocytes migrate from
neural crest following a
characteristic trajectory.
• They become functional by 3-4m & transfers melanosomes
to keratinocytes by 5th m.

37. In a nutshell…..
• The flat embryonic DEJ acquires skin specific
components by 8 wks,& all structures of mature
DEJ are in place by 12 wks.
• Skin appendages have both epidermal & dermal components
& reciprocal interactions b/n these two are central to their
development.
• Hair follicle progresses through the placode, presumptive
D.papillae, hair germ & hair peg stages to the mature follicle
while sebaceous gland development parallels hair follicle dev

38. THANK YOU !!