pH and Basic Chemistry for the Cosmetology Theory Exam

The four chemistry lines in the NIC theory outline

Basic chemistry is one of three areas inside Scientific Concepts, the domain worth 35% of the NIC National Cosmetology Theory Examination (bulletin effective July 1, 2022, revised January 1, 2026). The outline gives it four lines:

1. Recognize the purpose and effects of ingredients.
2. Recognize interactions between chemicals.
3. Recognize chemical reactions, with overexposure and chemical burn as the examples.
4. Recognize the values of the pH scale.

Every line starts with "recognize." Nothing in the outline asks you to balance equations. It asks you to read a situation, such as a product, a number, or a client's reaction, and know what it means for the service.

Reading the pH scale

The U.S. Geological Survey's explanation of pH is a clean starting point. The scale runs from 0 to 14, and 7 is neutral. Values below 7 are acidic, and values above 7 are basic, also called alkaline. pH measures the relative amount of free hydrogen ions and hydroxyl ions: more hydrogen ions means more acidic, more hydroxyl ions means more alkaline.

One detail from the same page makes a good trap question: only a solution that contains water has a pH. USGS gives vegetable oil and pure alcohol as examples of liquids that have no pH. So a pure oil treatment with no water in it does not have a pH at all.

The tenfold math, done slowly

pH is a logarithmic scale. USGS puts it this way: each number represents a tenfold change, so water at pH 5 is ten times more acidic than water at pH 6. The jump multiplies with every step:

USGS's own example sits on the last row: mine drainage at pH 2 is 100,000 times more acidic than neutral water at pH 7.

Worked example 1. A lotion is at pH 10. How many times more alkaline is it than neutral water? Count the steps from 7 to 10: three. Multiply 10 three times: 1,000.

Worked example 2. Product A is at pH 4.5 and product B at pH 5.5. Which is more acidic, and by how much? The lower number is more acidic, so A. The difference is one step, so A is 10 times more acidic.

Two mistakes cost points here. The first is subtracting and stopping: a gap of 3 is not "3 times stronger," it is 1,000 times. The second is reading the scale as a straight line. A product at pH 14 is not "twice as alkaline" as one at pH 7. It is seven steps away, ten million times. Half-steps follow the same rule: half a step is a factor of about 3.2, not 5, because 3.2 × 3.2 is about 10. Numbers like these are easier on recall, and flashcards planned for full cosmetology prep include pH.

Acid and alkaline effects on hair and skin

The 2015 review "Hair Cosmetics: An Overview" in the International Journal of Trichology explains why pH matters to a cosmetologist. Hair is sensitive to pH changes, and alkaline solutions swell the fibers and open the cuticle scales. That opening is what lets some products reach the cortex. Other points from the review and from a 2014 article by the same lead author:

The review adds a charge effect that explains conditioners. A higher-pH product leaves a net negative charge on the hair surface, and conditioners work by adding positive charges that neutralize it. The review adds that bleached and chemically treated hair has a higher affinity for conditioning ingredients.

On skin, strong alkalis are a burn risk. The Cosmetic Ingredient Review, an industry-funded expert panel whose safety assessments the FDA takes into account, describes sodium, potassium, and calcium hydroxide as caustic agents that can cause severe burns, and concludes they are safe in hair straighteners only under recommended use, with skin contact minimized. The FDA's fact sheet on dyes and relaxers says the same thing in practical terms: avoid applying a relaxer to the scalp and other skin, because it can irritate or burn. The 2015 review notes that petrolatum is applied along the hairline and on the ears before a relaxer to prevent alkaline burns.

Chemical reactions and interactions the exam expects you to recognize

Oxidation shows up in two places you already know. The 2015 review describes permanent dyeing as an oxidation reaction that lets pigments enter the cortex, and it describes hydrogen peroxide as the neutralizer after a thio straightening service. The chemical texture guide follows those reactions through relaxers and perms, and the haircolor theory guide follows them through color. Reaction items reward the safe call, and explanations planned for full prep link each one to FDA guidance.

A five-question pH and chemistry drill

These are Passy practice questions. Answer each one before reading the key below the list.

1. Which is more acidic, pH 6 or pH 4, and by how many times?
2. A lotion at pH 11 is how many times more alkaline than one at pH 8?
3. Does a pure almond oil treatment have a pH?
4. Why does permanent hair color need an alkaline formula?
5. A client feels stinging at the hairline eight minutes into a relaxer. Which outline line does this test, and what do you do first?

Key. (1) pH 4, 100 times, because two steps is 10 × 10. (2) 1,000 times, three steps. (3) No. Only a solution containing water has a pH, and almond oil is a vegetable oil. (4) Alkalinity swells the hair and opens the cuticle so the dye can reach the cortex. (5) "Recognize chemical reactions": stop and rinse the product out right away, then check the skin.

If you got question 1 or 2 wrong, rework the table above before moving on. Then work the pH-scale math question in the free 20-item cosmetology sampler to see the same reasoning in four-option form, with the logic behind each wrong answer explained.

Where chemistry questions overlap with safety

Several of the reactions above are also safety questions. Who requires a safety data sheet, which section covers a product's properties and reactivity, and who regulates the air in a salon are covered in the OSHA, EPA, and SDS guide.

The burning-scalp row in the reactions table is the one most worth rehearsing, because every tempting wrong answer keeps the chemical on the skin a little longer. The free mixed set has a relaxer scenario built on that decision, so you can test the stop-and-rinse reaction call in the free cosmetology theory set and compare your reasoning with the explanation for each option. Chemistry is one of three areas in Scientific Concepts, the domain behind 298 of the 850 questions planned for launch.