The skin is the largest organ of the body, making up 16% of body weight, with a surface area of 1.8 m2. It has three main layers, the epidermis, the dermis and the subcutaneous layer/hypodermis. Skin is a dynamic organ in a constant state of change, as cells of the outer layers are continuously shed and replaced by inner cells moving up to the surface.

• Epidermis acts as a physical and chemical barrier between the body and external environment.
• Dermis is the deeper layer providing the structural and nutritional support to the skin
• Subcutis or hypodermis is a loose connective tissue layer, which is an important depot of fat.

Hair is a filamentous biomaterial that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals.

Hair has two distinct structures:

• Hair follicle: This is the part beneath the skin. It is located in the dermis and maintains stem cells that re-grow the hair after it falls out.
• Shaft: This hard filamentous part extends above the skin surface.

A cross section of the hair fiber may be divided roughly into three zones:

• Cuticle:This is the outermost layer that consists of several layers of flat, thin cells laid out overlapping one another.
• Cortex:This is the middle layer that contains the keratin bundles.
• Medulla:This is the innermost layer.

• Nails consist of a dense plate of hardened keratin between 0.3 and 0.5mm thick.
• Fingernails function to protect the tip of the fingers and to help in grasping.
• The nail is made up of a nail bed, nail matrix and a nail plate.
• Nail matrix: composed of dividing keratinocytes, which mature and keratinize into the nail plate. The nail plate appears pink due to adjacent dermal capillaries and the white lunula at the base of the plate.
• Nail bed: It lies underneath the nail plate. The thickened epidermis which underlies the free margin of the nail at the proximal end is called the hyponychium.
• Fingernails grow at 0.1 mm per day; the toenails grow more slowly.