Basic Chemistry of Products: Practice Questions & Explanations

On the pH scale (which runs from 0 to 14), a value of 7 is neutral — neither acidic nor alkaline. Values below 7 are acidic (with 0 being the most acidic), and values above 7 are alkaline/basic (with 14 being the most alkaline). Pure water is neutral at pH 7. Healthy skin and hair are slightly acidic (around 4.5–5.5). Understanding the pH scale is essential in cosmetology because many products and chemical services depend on raising or lowering pH to achieve their effects.

The natural pH of healthy hair and skin is approximately 4.5 to 5.5, which is slightly acidic. This slight acidity, sometimes called the skin's 'acid mantle,' helps protect against bacteria and keeps the hair cuticle compact and smooth. Products designed to be 'pH balanced' aim to stay close to this range. Strongly alkaline products (like some relaxers) raise the pH and swell/open the cuticle, which is why an acidic neutralizing or balancing step is often needed afterward to restore the natural pH.

Because the pH scale is logarithmic, each whole-number change represents a tenfold change. So a pH of 8 is 10 times more alkaline than pH 7, and a pH of 9 is 100 times (10 × 10) more alkaline than pH 7. This is why even a seemingly small pH number difference can mean a large chemical difference in how a product affects hair and skin. Understanding the logarithmic nature of the pH scale is emphasized in the scientific-concepts portion of the exam.

A physical change alters the form or appearance of a substance without creating a new chemical substance (for example, melting ice, or wetting and drying hair to temporarily change its shape). A chemical change produces one or more new substances with different properties (for example, the action of a permanent wave or haircolor, which permanently alters the hair's structure). Many cosmetology services rely on chemical changes. Distinguishing physical from chemical changes is a basic chemistry concept on the exam.

An emulsion is a mixture of two liquids that normally do not mix — such as oil and water — combined and held together with the help of an emulsifier (a substance that keeps the droplets dispersed). Many cosmetic products, like lotions and creams, are emulsions. The emulsifier surrounds the droplets of one liquid so they stay suspended in the other rather than separating. Understanding emulsions and basic product chemistry helps cosmetologists understand how the products they use are formulated and behave.

A substance with a pH below 7 is acidic; the lower the number, the more strongly acidic it is. Substances with a pH above 7 are alkaline (basic), and pH 7 is neutral. In cosmetology, acidic products tend to contract and harden the hair cuticle (for example, acid-balanced or normalizing products), while alkaline products swell and open it (for example, many relaxers and some color). Correctly classifying substances as acidic, neutral, or alkaline by pH is essential basic chemistry for the exam.

Pure water is a neutral substance with a pH of 7 — neither acidic nor alkaline. It serves as the reference point for the pH scale. In cosmetology, water is also the most common solvent, used to dilute and mix many products. (Tap water may vary slightly due to dissolved minerals, but pure water is defined as neutral.) Recognizing pure water as the pH-7 neutral standard is a basic chemistry fact within the scientific-concepts content of the licensing exam.

A strongly alkaline service such as a chemical relaxer raises the hair's pH and swells/opens the cuticle to restructure the hair. Afterward, a neutralizing or acid-balanced step (for example, an acid-balanced shampoo) is used to bring the hair's pH back down toward its natural slightly acidic range (4.5–5.5), stop the chemical action, and help the cuticle close. Skipping this step can leave hair damaged and over-processed. Understanding pH and neutralization in chemical services is emphasized in the exam's chemistry content.

A 'pH-balanced' product is one formulated to stay close to the natural slightly acidic pH of hair and skin, roughly 4.5 to 5.5. Keeping a product in this range helps maintain the skin's protective acid mantle and keeps the hair cuticle smooth and compact, reducing damage. Many shampoos and skin products are marketed as pH-balanced for this reason. Understanding what pH-balanced means — and why staying near the natural pH matters — connects the chemistry and skin/hair-science content of the exam.