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The pH scale runs from 0 to 14. A value of 7 is neutral (the pH of pure water). Below 7 is acidic; above 7 is alkaline.

Healthy hair and skin sit in a slightly acidic range of about 4.5 to 5.5. This is often called the acid mantle and helps protect against bacteria and moisture loss.

The pH scale is logarithmic, so each whole number is a tenfold change. Two units (pH 5 to pH 7) means the solution is 10 x 10 = 100 times less acidic.

Sodium hydroxide relaxers are very alkaline, with a pH of about 12 to 14. The high pH swells and breaks disulfide bonds quickly, so processing must be timed carefully to avoid scalp burns.

No-lye relaxers most commonly use guanidine hydroxide (mixed on site from calcium hydroxide and guanidine carbonate). They are generally less irritating to the scalp but can leave more mineral deposits, making hair feel drier.

Permanent waving and chemical relaxing both break and reform the disulfide bonds in keratin. Hydrogen and salt bonds are only temporarily broken by water or heat styling.

Cold waves use ammonium thioglycolate (ATG) as the waving lotion. It is a reducing agent that breaks disulfide bonds at room temperature. The neutralizer (usually hydrogen peroxide or sodium bromate) then re-forms the bonds in the new shape.

The neutralizer (typically hydrogen peroxide) oxidizes the broken disulfide bonds, allowing them to re-form in the curled shape. Even though the product is called a 'neutralizer,' the chemistry is an oxidation reaction.

Temporary colors (rinses, color sprays, gels) coat only the cuticle and rinse out in one to two shampoos. They do not penetrate the cortex.

Permanent (oxidative) color is mixed with a developer (hydrogen peroxide). It penetrates the cortex, lightens existing melanin, and deposits new color molecules that are too large to wash out.

Demi-permanent (deposit-only) color uses a low-volume developer (typically 5 to 10 volume). It deposits color, gives slight conditioning, and fades gradually with no significant lift.

Developer volume refers to the volume of oxygen gas released per volume of peroxide. 10 volume means each unit of peroxide releases 10 units of oxygen. Higher volume = more lift.

10 volume developer (about 3% hydrogen peroxide) deposits color and tones without lifting. 20 vol gives one to two levels of lift; 30 vol gives two to three; 40 vol gives the maximum lift used for high-lift color.

20 volume developer is approximately 6% hydrogen peroxide. 10 vol is about 3%, 30 vol about 9%, and 40 vol about 12%.

A 1:2 ratio means two parts developer for every one part color. 2 oz color x 2 = 4 oz developer.

Shampoos clean using surfactants (surface-active agents). One end of the molecule attracts water (hydrophilic) and the other attracts oil and dirt (lipophilic), allowing soils to be rinsed away.

pH-balanced shampoos are formulated to roughly match the natural pH of hair and skin (about 4.5 to 5.5). This helps the cuticle lie flat and reduces dryness and irritation.

Clarifying shampoos contain stronger surfactants or chelating agents that remove hard-water minerals, chlorine, and styling product residue. They are useful before chemical services but can be drying with frequent use.

AHAs are water-soluble acids that loosen the bonds between dead surface skin cells (corneocytes), promoting gentle exfoliation. They work on the surface of the stratum corneum, not in the dermis.

Salicylic acid (BHA) is oil-soluble, so it can penetrate through sebum into pores. This makes it useful for oily and acne-prone skin to clear clogged follicles.

Retinoids speed up cell turnover and stimulate collagen and elastin production, making them popular for anti-aging and acne treatment. They can cause dryness and increased sun sensitivity.

SPF (Sun Protection Factor) measures protection against UVB rays, which cause sunburn. For UVA protection (which causes aging), look for 'broad-spectrum' on the label.

8 CCR §5194 requires employers to maintain an SDS for each hazardous chemical present in the workplace and to make them readily accessible to employees during their shift.

GHS-formatted SDSs have 16 standardized sections, ranging from product identification (Section 1) to other information (Section 16), including first aid, handling, and toxicology.

Business and Professions Code §7315 prohibits the use of MMA liquid monomer on clients in California. Ethyl methacrylate (EMA) is the legal alternative for acrylic nail systems.

Low-porosity hair has tightly packed cuticle scales that resist absorbing water and chemicals. It may require longer processing or a presoftener. High-porosity hair absorbs and releases chemicals quickly.

A strand test (also called a test curl) shows how the client's hair will respond to the wave solution so the stylist can choose the right product and time, preventing over- or under-processing.

16 CCR §979 requires products to be properly labeled and stored in clean, dry areas, separate from food, and in closed containers when not in use to avoid contamination or spills.

SDS Section 13 covers disposal. Used chemicals must be disposed of according to the manufacturer's directions and local hazardous-waste regulations, not into storm drains or open containers.

Section 4 (First-Aid Measures) of a GHS-formatted SDS lists the immediate steps to take for eye, skin, inhalation, and ingestion exposure.

Acidic finishing rinses bring the hair back toward its natural pH (around 4.5 to 5.5). This helps the cuticle close, locks in color, and reduces frizz.

The pH scale is logarithmic and inverted: each whole-number drop multiplies hydrogen-ion concentration by 10. Going from pH 6 to pH 3 is a 3-unit drop, so 10 x 10 x 10 = 1,000 times more hydrogen ions.

Alkaline solutions (pH above the natural 4.5 to 5.5 range) swell the hair shaft and lift the imbricated cuticle scales. The raised cuticle is what allows oxidative color, lighteners, and waving solutions to reach the cortex.

A 1:2 powder-to-developer ratio means two parts developer per one part powder. 1 oz powder x 2 = 2 oz developer. Using less developer than directed produces a stiff, dry paste that overheats and can scorch hair.

Volume rating divided by roughly 3.3 gives the percent peroxide: 10 vol is about 3%, 20 vol about 6%, 30 vol about 9%, and 40 vol about 12%. 40 vol is reserved for high-lift permanent color and is not used for on-scalp bleach.

Sulfite (acid) waves use ammonium sulfite or bisulfite at a pH near 6.5 to 7. They swell the hair less than alkaline thio waves, so they create a softer curl and are gentler on porous or color-treated hair, though processing time is longer.

Anionic surfactants such as sodium lauryl sulfate carry a negative charge and produce strong lather and grease removal, so they are the main cleansing detergents. Cationic agents condition, amphoterics are mild, and nonionics are used as emulsifiers and solubilizers.

Cationic (positively charged) surfactants are attracted to the negatively charged sites on damaged hair. They neutralize static, smooth the cuticle, and help detangling, which is exactly what conditioners are designed to do.

Both are anionic sulfate cleansers, but SLES has been ethoxylated (extra polyethylene glycol units inserted into the molecule). The added bulk makes SLES gentler on skin and eyes than the smaller, more aggressive SLS while keeping good foam.

Glycerin is a classic humectant; its hydroxyl groups bind water molecules and pull them toward the stratum corneum. Mineral oil is an occlusive, zinc oxide is a physical sunscreen, and benzoyl peroxide is an acne-fighting oxidizer.

Glycolic acid has the smallest molecular size of the common AHAs, so it penetrates fastest and deepest. Lactic acid is larger and is preferred when extra hydration is desired; mandelic and citric acids are larger still and act more gently on the surface.

Retinoids must be converted into retinoic acid in the skin to act. Retinol takes two conversion steps, retinaldehyde takes one, and tretinoin (retinoic acid) is already active. Fewer steps means stronger and faster effect at the same percentage.

SPF math: SPF 15 blocks about 93% of UVB, SPF 30 about 97%, and SPF 50 about 98%. The jump from 30 to 50 only adds 1 percent more protection, so reapplication every two hours matters more than chasing a higher number.

Physical (mineral) sunscreens use zinc oxide and/or titanium dioxide to sit on the skin and reflect or scatter UV light. The other ingredients listed are organic UV filters that absorb UV energy and convert it to heat, defining chemical sunscreens.

Section 1 (Identification) of the GHS 16-section SDS lists the product identifier, manufacturer name, address, and emergency phone number. Cal/OSHA's 8 CCR §5194 requires this sheet to be accessible to every employee on shift.

Section 8 of a GHS-formatted SDS gives exposure limits and the engineering controls and personal protective equipment (gloves, eye protection, ventilation, respirator if needed) that the employer must provide under 8 CCR §5194.

In an oil-in-water emulsion, tiny oil droplets are suspended in a much larger continuous water phase, stabilized by an emulsifier. O/W products feel lighter and less greasy, which is why they dominate lotions and rinse-out conditioners. W/O is the reverse (water-in-oil) and feels heavier.

Once color and peroxide are combined, the oxidation reaction begins. The mixture loses strength, can build dangerous pressure if sealed in a bottle, and is unsafe to apply later. Mix only what you need and discard leftover per the SDS.

MMA's smaller molecular size lets it diffuse into the nail plate and surrounding skin, increasing sensitization risk, and it cures into an extremely hard, inflexible film that can tear the natural nail off if bumped. For these reasons California's BPC §7315 bans MMA monomer on clients; EMA is the legal acrylic monomer.

Hyaluronic acid is a naturally occurring polysaccharide that can hold many times its weight in water in the upper epidermis, plumping dehydrated skin without occluding it. Petrolatum and beeswax are occlusive sealers; stearic acid is mainly a thickener.