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Proverbs 18:17 The man who first puts his cause before the judge seems to be in the right; but then his neighbour comes and puts his cause in its true light.

Hair Follicle Structure
Hair is mainly composed of the protein keratin. Keratin is made of rope-like intermediate filaments. The structure of the filaments provides strength to the hair shaft. Like other proteins, keratin is non-polar and is not miscible in polar substances, like water. For this reason, hair is waterproof.

Hair growth begins under the skin at the root. Each individual strand of hair is housed in a hair follicle. Only the “living” portion of the hair is found in the follicle. The hair that is visible is considered dead and is called terminal hair. The base of the root is called the bulb, which contains the matrix and the papilla. These two structures promote hair growth. Other structures of the hair follicle include the sebaceous gland and the erector pili muscles, which, respectively, produce a natural oil, called sebum, so that the shaft does not dry out, and are responsible for causing goose bumps.

Strand of human hair
Each strand of hair is made up of the medulla, cortex, and cuticle. The medulla is the innermost region of the hair strand and reflects light to give hair its various colors and tones. Finer hairs and naturally blond hairs have a fragmented or nonexistent medulla layer. Like the medulla, the cortex, or middle layer of the hair, contributes to hair color. The cortex contains melanin, which predisposes hair color based on the type of melanin that is present. The presence of eumelanin suggests brown or black hair, while pheomelanin suggests red hair. Blond hair is the result of having little pigmentation in the hair strand. The cortex also determines the shape of the hair strand. If the cortex is round, the hair is straight and if it is oval-shaped, the hair is wavy or curly. The cuticle coats and protects the hair strand.

Main article: Human hair color
All natural hair colours are the result of two types of hair pigment. Both these pigments are a type of melanin produced inside the hair follicle: Phaeomelanin is responsible for the yellowish-blond to red colors and Eumelanin is responsible for the brown to black shades. Gray hair occurs when these melanin molecules are no longer produced, so there is no pigment left to colour the hair naturally.

Main article: Human hair growth
Human hair grows everywhere on the body except for the palms of the hands, soles of the feet, the lips, and the eyelids, apart from eyelashes. Like skin, hair is an epithelium. Unlike skin, it is stratified, squamous, keratinized epithelium because it is made of multi-layered, flat cells and contains the protein keratin, whose rope-like filaments provide structure and strength to the hair shaft.

Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen phases. Each phase has specific characteristics that determine the length of the hair. All three phases occur simultaneously; one strand of hair may be in the anagen phase, while another is in the telogen phase.
The body has different types of hair, including vellus hair and androgenic hair, each with its own type of cellular construction. The different construction gives the hair unique characteristics, serving specific purposes, mainly warmth and protection.

SODIUM HYDROXIDE

Description

Sodium hydroxide is odorless and exists as a solid or a liquid. In solid form it is a white substance available in many forms, including lumps, sticks, pellets, and chips. It rapidly absorbs carbon dioxide and water from the air, and is very caustic to animal and vegetable tissue and to aluminum metal in the presence of moisture. Sodium hydroxide can be dissolved in water, alcohol, and glycerol, and generates heat while dissolving (Merck, 1989).

Physical Properties of Sodium Hydroxide

Molecular Weight	40.00
Boiling Point	1390 oC
Melting Point	318.4 oC
Vapor Pressure	1 mm at 739 oC
Density/Specific Gravity	2.120 at 20/4 oC (water = 1)
Log Octanol/Water Partition Coefficient	Too low to measure

SOURCES AND EMISSIONS

A. Sources

Sodium hydroxide is used to neutralize acids and make sodium salts, for example in petroleum refining it is used to remove sulfuric and organic acids. It is also used to hydrolyze fats in the production of soaps, and in the manufacture of rayon, textiles, and cellophane. Other uses include the manufacturing of plastics by dissolving casein, in reclaiming rubber by dissolving out the fabric, peeling fruits and vegetables in food production and in vegetable oil refining, and etching and electroplating. Sodium hydroxide also has applications in chemical and metal processing, the pulp and paper industry, disinfection, and to dehorn cattle (HSDB, 1991; Merck, 1989; Sax, 1987).

The primary stationary sources that have reported emissions of sodium hydroxide in California are pulp mills, public order and safety facilities, and manufacturers of aircraft and aircraft parts (ARB, 1997b).

Sodium hydroxide is registered as an adjuvant for agricultural use, and as an algaecide for use in industrial waste disposal systems and sewage systems. The licensing and regulation of pesticides for sale and use in California are the responsibility of the Department of Pesticide Regulation (DPR). Information presented in this fact sheet regarding the permitted pesticidal uses of sodium hydroxide has been collected from pesticide labels registered for use in California and from DPR's pesticide databases. This information reflects pesticide use and permitted uses in California as of October 15, 1996. For further information regarding the pesticidal uses of this compound, please contact the Pesticide Registration Branch of DPR (DPR, 1996).

B. Emissions

The total emissions of sodium hydroxide from stationary sources in California are estimated to be at least 770,000 pounds per year, based on data reported under the Air Toxics "Hot Spots" Program (AB 2588) (ARB, 1997b).

C. Natural Occurrence

No information about the natural occurrence of sodium hydroxide was found in the readily-available literature.

AMBIENT CONCENTRATIONS

INDOOR SOURCES AND CONCENTRATIONS

No information about the indoor sources and concentrations of sodium hydroxide was found in the readily-available literature.

ATMOSPHERIC PERSISTENCE

Sodium hydroxide is expected to be particle-associated or in the aerosol form in the atmosphere, and hence subject to wet and dry deposition. The average half-life and lifetime for particles and particle-associated chemicals in the troposphere is estimated to be about 3.5 to 10 days and 5 to 15 days, respectively (Balkanski et al., 1993; Atkinson, 1995).

AB 2588 RISK ASSESSMENT INFORMATION

The Office of Environmental Health Hazard Assessment reviews risk assessments submitted under the Air Toxics "Hot Spots" Program. Of the risk assessments reviewed as of December 1996, for non-cancer health effects, sodium hydroxide contributed to the total hazard index in 18 of the approximately 89 risk assessments reporting a total chronic hazard index greater than 1, and presented an individual hazard index greater than 1 in 3 of these risk assessments. Sodium hydroxide also contributed to the total hazard index in 17 of the approximately 107 risk assessments reporting a total acute hazard index greater than 1, and presented an individual hazard index greater than 1 in 9 of these risk assessments (OEHHA, 1996b).

HEALTH EFFECTS

Sodium hydroxide is caustic at the site of contact whether by inhalation, ingestion, or skin contact.

Non-Cancer: Fumes or mists of sodium hydroxide are strongly alkaline. Fumes and mists are very irritating to the eyes, skin, and upper respiratory tract. Severe exposures may result in pulmonary edema. Sodium hydroxide is neutralized at the site of contact and is therefore unlikely to cause effects elsewhere in the body (U.S. EPA, 1994a).

An acute non-cancer Reference Exposure Level (REL) of 20 micrograms per cubic meter (µg/m3) and a chronic non-cancer REL of 4.8 µg/m3 are listed for sodium hydroxide in the California Air Pollution Control Officers Association Air Toxics "Hot Spots" Program, Revised 1992 Risk Assessment Guidelines. The toxicological endpoints considered for chronic toxicity are the respiratory tract and skin. The acute toxicological endpoint is respiratory irritation (CAPCOA, 1993). The United States Environmental Protection Agency (U.S. EPA) has not established a Reference Concentration (RfC) for sodium hydroxide (U.S. EPA, 1995a).

Cancer: The International Agency for Research on Cancer and the U.S. EPA have not classified sodium hydroxide as to its carcinogenic potential (IARC, 1987a; U.S. EPA, 1995a).