In Charaka Samhita, Twacha (the word Twacha means skin) is defined as that which covers the body from outside. Anatomically.
Acharya Charaka has described 6 layers and the corresponding diseases of the skin.
Anatomical description, Charaka has also described the natural texture of skin in Prakriti (constitution) and Sara Praikshana (examination of excellence of skin tissue).
The outermost layer is the Udakadhara (containing watery substance or lymph). The second one holds the blood. The third layer is the seat of Sidhma (dermatitis) and Kilas Kushta (leucoderma). The fourth layer is the seat of Dadru Kushta (ringworm). The fifth layer produces Alaji (boil) and Vidradhi (abscess). The sixth and deepest layer is the origin of deep seated red and black colored boils and glands. Susrutha has described 7 layers of skin.