DIY face serums: What is safe to make at home?

What makes a mixture a useful face serum?

Serums are light liquids made with oil or water that deliver concentrated ingredients to the skin. They usually go after cleansing and before moisturizer. Choosing an ingredient is only part of making one: the base that carries it, the complete formulation and the ingredient's stability affect how well the serum works. Serum prices vary widely, but the ingredients matter more than the size of the receipt.1

Why storing a homemade serum is the difficult part

Bacteria and fungi can enter cosmetics through raw materials, water, other ingredients, preparation conditions or fingers dipped into a container. Inadequate packaging, storage and an ineffective preservation system also create opportunities for contamination. A homemade serum needs attention to all of these, not just a clean bottle. Injuries from contaminated cosmetics are uncommon, but they can be serious.2

Use these handling rules for cosmetic products:

• Wash your hands before application, especially before putting fingers into a container.
• Keep containers clean and do not share products.
• Do not add water or saliva to a finished cosmetic. This can introduce microorganisms and dilute its preservatives.
• Follow the manufacturer's storage instructions. Warm or damp conditions can encourage microbial growth, and preservatives can break down.
• Do not guess a storage life for a homemade batch without an established preservation system.

What should you leave out of DIY skincare?

Avoid lemon juice, lime juice and apple cider vinegar in homemade facial mixtures. Their low pH, meaning high acidity, can irritate skin. Advice about ingredients in a homemade mask is not a recipe for a serum you leave on every day or keep in a bottle.3

Do not apply undiluted essential oils directly to your face. They can cause sensitisation, meaning the immune system develops an allergy to a substance. Tea tree, lemongrass, sandalwood, clove and several other essential oils are recognised causes of allergic contact dermatitis, an itchy skin reaction triggered by contact. High concentrations can also cause irritation. Dilution is not a reason to use an oil you already know you are allergic to.4

Choose an ingredient for the result you want

These are ingredients to look for in formulated products, not instructions for mixing raw ingredients:

• For dry skin, consider hyaluronic acid or ceramides. Ceramides are fats that help keep moisture from escaping.
• For brown spots and signs of sun damage, vitamin C is an option. It can also stimulate production of collagen, a structural protein in skin.
• For uneven pigmentation, kojic acid and glycolic acid are options.
• For wrinkles, antioxidant ingredients such as resveratrol and tea polyphenols are options.

How to add a formulated serum to your routine

1. 1Test a small area before applying the serum widely.
2. 2Cleanse your face.
3. 3Apply the serum before moisturizer. A few drops typically cover the whole face.
4. 4Apply your moisturizer.

Cleansing, daily moisturizing and daily sunscreen remain the priorities, even when a homemade bottle is auditioning for the lead role. Keep those basics in place rather than treating a serum as the whole routine.3

Who should be especially careful?

Concentrated serum ingredients can irritate sensitive skin. Be cautious about combining acid containing serums with other acids, vitamin C with a retinol cream, or a retinol serum with a prescription retinol cream. These combinations can increase irritation.1

People with atopic dermatitis, a form of eczema, have an increased risk of allergic contact dermatitis from essential oils. A reaction can appear 24 to 72 hours after exposure, so an immediate lack of discomfort is not enough to rule it out. Watch for itching, redness and scaling, including symptoms that spread beyond where you applied the oil.4

Is there a simpler DIY option?

If you want a homemade skincare activity rather than a stored serum, one option is a sheet mask with your own moisturizer or aloe vera. This is a mask, not a serum formula. Test a small amount on the jawline or behind the ear before broader use. Face masks can give an immediate but temporary boost in hydration or appearance; that is different from a lasting treatment result.3

When should you stop using a mixture?

Stop exposure to an essential oil that causes itching, redness or scaling. Avoiding the allergenic oil usually allows symptoms to resolve, although some reactions persist. Seek medical assessment for a persistent rash; a dermatologist can use patch testing to identify contact allergens. If a cosmetic develops a bad smell or another sign of contamination, stop using it and report the problem to the FDA in the United States.24