Hair and nutrients for healthy hair

Introduction

Hair is a unique structure only found on all mammals including humans. It is considered as a skin accessory structure. Skin produces hair in different lengths, thickness, and texture almost all over the body surface except for a few areas of the body, i.e., sole of the foot, palm of the hand, buccal surface of the lip, and some parts of external genitalia. This topic is mainly focus on scalp hair.

Functions of Human Hair

Hair has many important functions as the following:

1) The main function is to insulate the human body in two ways. Firstly, it acts as a physical barrier between external cold air and the skin. Secondly, it also traps warm air in between the skin and the hair, keeping the body warmer.

2) To protect the skin from external environment and mechanical insults. For example, scalp hair prevents sunlight, cold, and physical damage to the head; eyebrows and eyelashes stop things entering the eyes.

3) To buffer against friction. For example, hair on the legs, genitals and underarms. Hair also soaks up sweat to ease evaporation and prevent skin from chafing and blistering.

4) To increase the perception of the skin surface for tactile stimuli. Movement or vibration of hair can stimulate sensory nerves within the skin.

Hair Anatomy (Figure 1)Hair is a very complicated structure. It is comprised of the root (or hair follicle)

inside the skin and the shaft (the visible dead part of hair) on the body surface. Hair shaft consists of three layers.

1) The outermost of hair shaft are the cuticle cells covering the hair from the root to the tip. They are colorless, at overlapping dead cells that give the hair shaft strength. The integrity and properties of this layer have an important role in protecting the hair cortex from physical and chemical insults.

2) The cortex, which contains pigment (melanin) that defines hair color. This layer is responsible for growth of hair shaft. It also represents the majority of the hair fiber composition and plays an important role in the physical and mechanical properties of hair. The cortex defines hair texture (i.e. straight hair and curly hair).

3) The medulla is the innermost layer (core) of the hair shaft. This layer is not present in all hairs, only found in thick coarse hairs.The cuticle, cortex and medulla are comprised largely of keratin, although it is structurally different in each layer.

There are approximately 5 million hair follicles on the human body with 100,000 on the scalp. The scalp has the greatest density of hair follicles with approximately 300 to 500 hairs per square centimeter. At the base of hair follicles, they enlarge into hair bulbs surrounding dermal papilla cells (hair papilla). These cells bear capillary vessels which send nutrients from blood to the hair. Other structures of the hair follicle include the oil producing sebaceous gland which lubricates the hair and the arrector pili muscles, which are responsible for causing hairs to stand up (goose bumps).