Cosmetic Chemistry – SS1 Beauty & Cosmetology Lesson Note (Third Term)

Cosmetic chemistry is the study of the chemicals that make up products such as soap, lotion, shampoo and facial serum.

Behavioural objectives

By the end of the lesson, students should be able to:

1. name the five basic types of ingredient in cosmetics and state the job of each;
2. compare natural and synthetic products, giving examples, advantages and disadvantages of each;
3. explain why sulphates, parabens and simple alcohols are sometimes avoided;
4. state the pH of the skin and explain why a product should be pH balanced;
5. show with a simple experiment how an emulsifier mixes oil and water.

What is a cosmetic ingredient?

A cosmetic ingredient is a chemical added to a product to give it a particular job.

• Clean: some ingredients remove dirt and oil, as in soap and shampoo.
• Add smell: some give the product a pleasant scent.
• Soften: some make the skin or hair feel soft and smooth.
• Hold together: some keep oil and water from separating.
• Protect the product: some stop it from spoiling on the shelf.

What are the five basic ingredients in every bottle?

The five basic types of cosmetic ingredient are water, emulsifiers, preservatives, emollients and fragrances.

1. Water (the base): it is usually the first item on a lotion or shampoo label, written as “Aqua”. It dissolves other ingredients and makes the product easy to spread.
2. Emulsifiers: they hold oil and water together. Without them, a cream separates into oily and watery layers.
3. Preservatives: they stop mould and bacteria from growing in the product. They keep it safe to use for a long time.
4. Emollients: they make the skin feel soft and silky by filling the tiny gaps between skin cells. Examples: coconut oil, shea butter and silicones.
5. Fragrances: they give the product its smell. They make it pleasant to use, but they are a common cause of skin allergies.

What is the difference between natural and synthetic products?

Natural products

Natural products are ingredients that come from plants, animals or minerals.

• Plant sources: aloe vera, shea butter and coconut oil.
• Animal source: honey.

Synthetic products

Synthetic products are ingredients made by chemists in a laboratory or factory.

• Preservatives: parabens are made in the laboratory.
• Other examples: petrolatum (Vaseline), mineral oil and synthetic dyes.

Comparison of natural and synthetic products

Which ingredients should a stylist watch out for?

Stylists should watch out for sulphates, parabens and simple alcohols, because they can be too harsh for some clients.

1. Sulphates: these are the cleansing agents that make shampoo foam. Too many can make natural hair very dry and brittle.
2. Parabens: these are common preservatives that keep bacteria away. Some people worry they are too strong for the body, so many products now say “Paraben-Free”.
3. Simple alcohols: ethanol and isopropyl alcohol can dry out the skin and hair very fast.

• Remember: not all alcohols are harsh. Fatty alcohols such as cetyl alcohol are used to soften and thicken creams.

What is pH and why must a product be pH balanced?

pH is a scale from 0 to 14 that shows how acidic or alkaline a substance is.

• Below 7: acidic.
• Exactly 7: neutral, as in pure water.
• Above 7: alkaline.
• Skin and hair: slightly acidic, at a pH of about 5.5.

Why pH balance matters

• Too alkaline: a very alkaline product, such as harsh laundry soap, strips away the skin’s natural protection.
• pH balanced: a product made close to the skin’s pH does not sting or irritate the client.
• Cosmetic chemist’s job: to adjust each product so that it suits the skin and hair.

How should a stylist read an ingredient label?

An ingredient label lists the contents of a product, usually from the largest amount to the smallest.

• First ingredients: the first few names on the list make up most of the product.
• Sensitive skin: choose products with fewer ingredients, especially without added fragrance.
• Long names: there is no need to memorise them. Learn the main groups taught in this lesson.
• “Natural” does not always mean “safe”: raw lemon juice is natural, but it can burn the skin if the skin is left in the sun.

Class practical activity

The oil and water experiment

1. Pour water into a clean jar, then add some vegetable oil. Watch the two stay in separate layers.
2. Add a squeeze of dishwashing soap, which acts as an emulsifier.
3. Close the jar and shake it.
4. Observe that the oil and water now mix. This shows how an emulsifier works in lotions and creams.

• Safety: the soap is for the demonstration only. Do not put it on the skin.

Label reading

1. Look at the back of a hand cream.
2. Check whether “Water” or “Aqua” is the first ingredient.
3. Find any natural ingredients, such as oils or plant extracts.
4. Find any fragrance or preservative listed.

Evaluation

1. List the five basic types of ingredient found in cosmetics.
2. What is the job of an emulsifier?
3. Give two examples each of natural and synthetic ingredients.
4. Why can too many sulphates be a problem for natural hair?
5. What is the pH of the skin, and why should a product be pH balanced?

Assignment

Draw a table with one advantage and one disadvantage of natural products and of synthetic products. Below it, explain why “natural” does not always mean “safe”, and give one example.