Cosmetic Chemistry II – SS3 Beauty & Cosmetology Lesson Note (Second Term)

Cosmetic Chemistry II is the study of how to make beauty products safe as well as effective.

• Preservation: keeps microbes out of products.
• Fragrance: makes a product smell pleasant without irritating the skin.
• Safety testing: proves a product is safe before a client uses it.

Behavioural objectives

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

1. state why beauty products need preservation;
2. explain what a preservative is and when one must be used;
3. name common types of preservative;
4. compare fragrance oils with essential oils and state the usual safe limit for fragrance in leave-on products;
5. describe the patch test, the stability test and the pH test;
6. list good laboratory habits for a cosmetic chemistry student.

Why do we need chemistry in beauty?

Chemistry explains how ingredients mix, why products spoil and how to keep them safe for the skin.

• Ingredients: creams and lotions are made of water, oils and nutrients.
• Risk: water and nutrients give bacteria, mould and yeast a place to grow.
• Goal: a product must be safe as well as effective.
• Example: a cream that makes the skin glow is a failure if it gives the client a fungal infection two weeks later.

What are the three guards of product safety?

1. Preservation: keeping germs away from the product.
2. Fragrance control: making the product smell pleasant without causing irritation.
3. Safety testing: proving the product is safe before it touches a human face.

What is preservation?

Preservation is the use of chemicals and clean working methods to stop microbes from spoiling a product.

• Everyday example: soup left on a table for three days in the heat smells bad and grows mould.
• Same risk: hair creams and face lotions contain water, so they spoil in a similar way.

What is a preservative?

A preservative is a chemical added to a product to stop the growth of microbes such as bacteria and mould.

• Hidden danger: a product without a preservative may look fine but be full of germs.

When must a preservative be used?

A preservative must be used whenever a product contains water or can let water get in.

• Water-based products: any product with water (listed as Aqua on the label) needs a preservative.
• Risky containers: a jar you dip wet fingers into, for example in the shower, lets water and germs in.
• Pure oil products: a 100% oil product such as a pure body oil does not always need a preservative.
• Antioxidants: oil products may need these to stop the oil smelling rank or old.

What are the common types of preservative?

There are three common types of preservative: parabens, phenoxyethanol and natural preservatives.

• Parabens: very common and effective, though some brands avoid them because customers prefer “natural” products.
• Phenoxyethanol: a popular preservative that kills bacteria.
• Natural preservatives: certain salts and plant-based ingredients, often weaker, so they must be used carefully.

What are the signs that a product has spoiled?

• Smell: a sour, rancid or “old” odour.
• Colour: a change from the original colour.
• Mould: spots or fuzzy growth on the surface.
• Texture: the oil and water separate, or the product becomes watery or lumpy.

What is the role of fragrance?

Fragrance is the scent added to a product to make it pleasant to use.

• First impression: it is usually the first thing a customer notices.
• Emotional link: a pleasant smell makes customers like the product.
• Chemistry: fragrance is one of the most complex parts of a formula.

What is the difference between fragrance oils and essential oils?

A fragrance oil is a scent made in a laboratory. An essential oil is a scent extracted from plants such as lavender or lemon.

What is the safe limit for fragrance?

In most leave-on products, fragrance is usually kept at 1% or less of the total mix.

• The 1% rule: in a face cream, fragrance should not be more than 1% of the total mix.
• Reason: fragrance is one of the most common causes of skin allergy in beauty products.
• Example: in 100 g of face cream, use no more than 1 g of fragrance.

What are sensitisers?

Sensitisers are ingredients that can irritate the skin or cause an allergic reaction.

• Cinnamon oil: can irritate the skin.
• Citrus oils: some, such as lemon and bergamot, can make the skin burn or darken in sunlight.

What is a masking scent?

A masking scent is a small amount of fragrance used to cover a bad smell from raw ingredients.

• Example: raw shea butter or certain chemicals may smell unpleasant.
• Result: the customer enjoys using the product.

How do we test a product for safety?

There are three basic safety tests: the patch test, the stability test and the pH test.

• Reason: a maker must test a product before selling it, and must never use customers as “guinea pigs”.

What is the patch test?

The patch test checks whether a product causes a reaction on the skin.

1. Clean a small area of skin, usually the inner arm.
2. Apply a small amount of the product.
3. Leave it for 24 to 48 hours.
4. Look for redness, itching or swelling.
5. If any reaction appears, wash the area and do not use the product.

What is stability testing?

Stability testing checks whether a product stays together in heat and cold.

• The heat test: put a sample in a very warm place for a few weeks. Check whether the oil separates from the water.
• The cold test: put a sample in a fridge. Check whether it becomes too hard to use.
• Pass mark: a stable product keeps the same texture and colour in both heat and cold.

What is pH testing?

pH testing measures how acidic or alkaline a product is. The skin is slightly acidic, usually around pH 5.5.

• pH strip: a paper strip that changes colour to show the pH.
• pH meter: an instrument that gives a pH reading.
• Kit: a pH strip or meter is an important part of your chemistry kit.

What lab habits should students keep?

Good lab habits are the working rules that a cosmetic chemistry student follows like a scientist.

1. Documentation: keep a “batch book” and write down the grams of each ingredient used. A good product can then be repeated.
2. Contamination control: never mix with wooden spoons, because wood holds bacteria. Use stainless steel or glass.
3. Labelling samples: put the date and the formula name on every test bottle.
4. Sourcing ingredients: buy chemicals and oils only from trusted suppliers. Cheap chemicals often contain impurities that can ruin your work.

Evaluation

1. What is a preservative, and when must one be used?
2. Name three types of preservative.
3. State two differences between fragrance oils and essential oils.
4. What is the 1% rule for fragrance?
5. Describe how to carry out a patch test.

Assignment

Write a one-page safety guide for a new beauty student. It should explain the heat test and the cold test, say why pH testing matters and give the usual pH of the skin. It should also list the four items on the professional lab checklist with one reason for each.