The Scientific Guide to Curly Hair

Curls are the coolest, but because no two curly heads are alike, it can take a lot of trial and error to find the haircare routine that’s ideal for you. 

We’ve written this guide to help demystify curly hair, using science to help take the guesswork out of caring for your curls. You’ll see that it’s not so complicated - and that you can achieve great things with the right products, washing less, and detangling and drying with care.

The STAM system

Over 60% of the world’s population has curly hair, yet most research to date has clumped hair into three catchall types - African, Asian, and Caucasian. Based on highly flawed assumptions, this broad and problematic categorisation does not account for the complexity and diversity of people or their hair. 

A more representative and useful scientific classification system, STAM, categorises hair into eight types from I to VIII, based on hair curvature rather than race. STAM uses four measurements: 

1. Curl diameter
2. The number of waves within a certain distance on a hair strand.
3. The number of twists/constrictions within a certain distance on a stretched hair strand. 
4. The ratio between the length of hair in its natural state and stretched. 

So, based on how hair measures up, it is classified into one of the following eight types: Type I is straight; Type II is loose waves; Type III is wavy; Type IV is curly; Type V is very curly; Type VI is coily; Type VII is tight coils; and Type VIII is zig-zag coils.

But don’t worry, you don’t need to pull out a ruler and start counting waves. Use the visual guide below to determine your hair type. You will probably have two or more curl types, but one will be the most predominant. Why is it necessary to categorise your hair? Because the type of curl determines the appearance, porosity, weak points, and specific grooming needs of your hair. 

Curls are sensitive and need TLC.

All curly hair types (IV to VIII) have a lower tensile strength (the stress that hair can withstand while being stretched before breaking) than wavy or straight hair types, so they need specialised care. The curlier the hair, the more weak points it has, and the more vulnerable it is to breakage and heat damage. 

The unique shape of coily hair types (VI-VIII) makes untangling and combing especially difficult when hair is dry. Research has found that breakage is significantly reduced if coily hair is combed and detangled when wet. 

The twists and turns of curly hair also make it difficult for the scalp's natural oils (sebum) to travel and lubricate the entire length. A lack of oil can make hair dry, frizzy and more prone to tangling. 

Porosity 

Porosity refers to your hairs’ ability to absorb and release water. Curly hair is naturally more porous, making it susceptible to the effects of humidity. 

In humid weather, hair absorbs water, which can cause swelling, increased volume and frizz. The extra moisture can actually be great for some curl types; generally IV, VII, and VIII curls respond well to moderate humidity without getting frizzy. However, when the air is dry, curls can lose their moisture - making hair prone to breaking and split-ends. 

So, what does curly hair need? 

Moisture. Protein. Oils.Moisture 

Moisture deficiency is a common and avoidable cause of hair breakage. The best way to replenish and keep hair hydrated is with a leave-in product. Hair moisturisers can be gels, milks, lotions, or creams; they contain humectants that attract and maintain moisture, and emollients and oils to seal the moisture in. 

IV-V hair types should try gel, milk or lotion products. If your hair is fine, gels and milks are best. VI-VIII hair types can use heavier products like lotions or creams:

Keep an eye out for these naturally-derived ingredients to keep your curls moisturised. 

• Humectants: Glycerin, Sodium PCA, Propanediol, Panthenol, Sorbitol
• Emollients: Coco-Caprylate, Caprylic/Capric Triglyceride, Ceramides, Cetyl Alcohol, Cetearyl Alcohol, Squalane, Lecithin, Glyceryl Oleate. 

Protein 

Proteins help to increase tensile strength, reduce breakage and smooth hair. Proteins and amino acids work by binding and filling in damaged areas of the cuticle. Amino acids and small protein fractions can also penetrate the cuticle to improve the internal strength of damaged hair. 

• If you don’t colour, chemically treat or use heat: a protein containing shampoo, conditioner and regular treatment should be sufficient for your care routine. 
• If you colour or regularly use heat: a protein containing shampoo, conditioner and leave-in product is a good idea. 
• If you lighten or chemically treat your hair; a protein containing shampoo, conditioner, leave-in and regular intensive treatment with a high protein concentration is a must.

Keep an eye out for products that contain:

• Hydrolysed proteins like wheat, almond, soy, rice, pea, and oat. 
• Or amino acids like arginine, glycine, cysteine, phenylalanine.

Oils

Oils are fantastic for curly hair, and because sebum can’t traverse curls easily, it’s essential to apply oils regularly. Oils lubricate hair, which reduces friction between strands; preventing tangles and breakage. Oils also seal in moisture, promote shine and smooth frizz.   

Some natural oils like coconut and babassu have a natural affinity for hair protein and are proven to penetrate the hair shaft; minimising swelling and preventing protein loss. These oils are great for every curl type but especially highly porous or damaged hair.   

Shea Butter is brilliant for improving curl elasticity. Jojoba Oil is a liquid wax that mimics sebum, and Castor Oil is great for shine. 

If you find using natural oils too heavy, apply them to dry hair for 20min-overnight as a pre-wash treatment instead. There are also naturally-derived silicone alternatives (e.g. Undecane, Tridecane, Coco-Caprylate, Diheptyl Succinate, Capryloyl Glycerin/Sebacic Acid Copolymer) available and these work well in leave-in products for curls that are easily weighed down. 

Water-insoluble silicones like dimethicone should be avoided as they buildup on the hair and require harsh detergents to remove, which also strip curls of their moisture. 

Botaniq Elixir Lux is a lightweight oil that combines botanical lipids with biotech actives to replenish and protect all hair types and is a great addition to your curly hair regimen for longterm healthy hair. 

Wash RoutineGentle Cleansing  

As a general rule, the less you wash curly hair, the better. Once a week or less is suitable for most curl types. 

Always use a sulfate-free shampoo to remove product residue without stripping hair of its natural oils. If you choose to co-wash, it’s imperative that you still cleanse with shampoo once a month to remove buildup from your hair and scalp. 

Conditioning 

Conditioners are based on cationic ingredients that stick to hair through electrostatic attraction. Choose a conditioner that also replenishes the hair with oils and proteins to restore the hair surface and protect damaged areas.   

If you find conditioner isn’t nourishing enough for your curls, replace it with a mask. A mask contains higher concentrations of oils and active ingredients. 

Detangling 

You can detangle your hair just before you wash and/or while you condition. Make sure your strands are coated in conditioner, a leave-in detangler or oil. 

Begin detangling from the ends first and then work your way up - be gentle. Use a wide-tooth comb in wet hair or natural fibre brush if your hair is dry. Always detangle VI-VIII types when hair is wet.  

Drying

Swap your towel for an old cotton t-shirt to dry your hair. The rough fibres of an ordinary bath towel will rough up your cuticle, encouraging frizz. Sleeping on a silk or satin pillowcase will also prevent curls from frizzing and tangling during the night. 

It’s all about treating your hair (and yourself!) with TLC. Make sure you’ve got a great balance of moisture, protein and oils, that you’re cleansing rarely and gently, that you’re using products that are kind to your curls, and detangling and drying with care.

  

References

Cornwell, P and Malinauskyte, E. “Defying damage: understanding breakage in afro-textured hair.” Cosmetics & Toiletries Magazine, Feb, 21-29 (2020).  

De la Mettrie, Roland et al. “Shape variability and classification of human hair: a worldwide approach.” Human biology vol. 79,3 (2007): 265-81. 

Draelos, Z D. “The biology of hair care.” Dermatologic clinics vol. 18,4 (2000): 651-8.

Robbins, C. “Chemical and physical behavior of human hair.” 4th ed. Springer (2002).

Ruetsch, S B et al. “Secondary ion mass spectrometric investigation of penetration of coconut and mineral oils into human hair fibers: relevance to hair damage.” Journal of cosmetic science vol. 52,3 (2001): 169-84.