While some believe deep conditioning is a must-do step in the curly hair care routine, others agree it depends on your hair type. This debate has been long-standing. And if you have curly hair, you’re probably also wondering if deep conditioning is necessary for everyone with curly hair.
Deep conditioning is one of the most essential steps in a curly hair regimen. Curly hair is typically on the dry side, and due to the texture curl patterns, naturally produced sebum does not efficiently run down the strands. A deep conditioner can restore moisture and repair damage caused by dryness.
Let’s explore the necessity of deep conditioning for those with curly hair, whether all curly types require it. We also discuss how long deep conditioning should be done, what ingredients are best, and why it is beneficial during hair care.
Deep Conditioning – A Highly Regarded Treatment for Curly Hair
Curlies favor deep conditioners, which are available in a range of treatments on the market. We’ve been taught that deep conditioners are one of the most critical curly hair care steps to practice once a week. We also learn to leave them in for 20 – 30 minutes and then rinse them.
Deep conditioning hair is frequently advised by hairstylists and experts, especially for clients with brittle, damaged, or porous hair. Additionally, with the influx of curly girl hair trends and a newfound love and acceptance for natural curls, deep conditioning is a recurring topic within the curly hair world.
A general perception of a deep conditioning treatment is that it is a “more concentrated formulation,” offers better “penetration of active ingredients,” and provides “superior hair quality in the end.”
There are several fundamental questions regarding “Deep Conditioning” curly hair, and we attempt to help you understand the science behind it in the following points.
What is Deep Conditioning?
Conditioning is defined as making something behave in a certain way. It applies to hair by using a product that causes it to do certain things, like become softer, smoother, less tangled, more nourished, etc. This allows the hair to be styled easier, look shinier, and have less frizz.
Deep conditioning goes a step further and allows the product to penetrate the hair fibers, feeding the hair. This deeply nourishes your hair and helps to restore moisture and repair damage. The treatment is frequently used on damaged hair fibers to restore mechanical strength and ease manageability.
Damaged hair is highly porous, frizzy, and susceptible to break during daily combing, brushing, or styling. Damage often occurs during sleeping, washing, and drying. Chemical treatments such as bleaching, perms, or straightening may also result in significant hair damage.
Prolonged and repeated exposure to sunlight also damages hair fibers. Your hair loses its proteins and becomes weak. Microscopic examinations of the hair surface reveal cracks along the hair shaft and deep inside the hair cortex structure.
Deep conditioning treatments are vital to restore your hair quality and improve its overall health when these elements of damage are present in your hair. It is an excellent way to recover and repair the hair’s mechanical strength.
Why Deep Conditioning is Necessary for Curly Hair
Not every curly hair type needs deep conditioning regularly. But since curly hair tends to be drier than other types, it is important to make it a part of your hair care routine. The curlier types, especially from types 3 and 4 tend to require frequent deep conditioning to maintain hair health.
Curly hair is considered textured hair. The curly pattern (coils, twirls, twists, etc.) from the Z and S-shapes creates a challenge for natural moisture from sebum production to pass through the strands. This can often leave your hair dry, brittle, fragile, and all sorts of damage.
Comparing curly hair to straight and wavy types, deep conditioning from products is essential and helps repair damage and restore moisture loss or provide nourishment when it is lacking. It might not be necessary for everyone, but deep conditioning can be vital for most curly hair types.
Is Deep Conditioning a Myth?
Deep conditioning is not a myth. It is a scientific topic, and there are clear shreds of evidence supporting the penetration of active molecules.
Scientists have discovered the possible mechanism of hair conditioning, describing how different hair conditioning agents interact with hair cuticles and can even penetrate hair fiber. Various reports have examined the mechanism of deep conditioning and how active ingredients work inside the hair fiber. 1–2
Does Deep Conditioning Actually Work?
Understanding what deep conditioning is and knowing if it actually works are two different things. Only once you fully comprehend how and why deep conditioning works can you believe its magic and make it a staple in your weekly hair care regimen. To understand that deep conditioning does work, you must understand how deep conditioners interact with your hair cuticles.
The Effect of Deep Conditioning on Hair Cuticles
Cuticles are the first point of interaction for hair conditioning agents. Most conditioning ingredients stick to the hair surface during this initial interaction and do not penetrate.
Cationic surfactants and polymers are the most common conditioners used and found in deep conditioning products. They interact with the negatively charged hair surface, and this interaction is responsible for improving shine, smoothness, detangling, and combability.
However, small conditioning molecules can penetrate the cuticle openings deep into the hair cortex. They pass through the tiny spaces among the cuticle layers leading to the inner core of the cortex.
The diffusion of these ingredients is strictly controlled by “SIZE” and “CONCENTRATION GRADIENT.”3-4 The hair care industry has developed various molecules penetrating hair fibers. A tentative list of these ingredients is discussed later.
Molecular Size and Shape of the Active Molecule
Cuticle pores are tiny. The microscopic examination reveals that only molecules of a specific size and shape can pass through them. The diffusion of active ingredients is also facilitated by the expansion or quick opening of the cuticle pores.
Water absorption is known to help pore opening and thus boost active ingredient diffusion. These conditioning molecules pass through the cuticle layers and finally enter the cortex. Chemically treated and damaged hair fibers have wider cuticle pore size making it easier for molecules to diffuse through.
Ingredients that Can Diffuse During Deep Conditioning
As mentioned, the diffusion ability of a substance is determined by its molecular size and shape. Large molecules with greater positive charge stick to the cuticle layers and cannot penetrate the hair. Smaller and more fragmented molecules, having a non-ionic or lipid-based nature, have a greater possibility to diffuse.
To get an idea of ingredients that may enter the hair cortex, check out this empirical list:
Surfactants
Anionic surfactants, such as sodium lauryl sulfate or sodium laureth sulfate, carry a negative charge and effectively clean hair. Most of these ingredients are water-soluble, mostly stay outside, and, being anionic, are easy to rinse off.
But remember, some sulfates are harsh chemicals and may strip off essential lipids from the surface, leaving your hair dry and frizzy.
Cationic Polymers
Cationic polymers, such as Guar Hydroxypropyltrimonium Chloride or Polyquaternium-10 and Polyquaternium-7, carry a positive charge and stick to harmful amino acid sites at the hair shaft. Most cationic found in market formulations are large molecules in size and have large positive charge density; therefore, they stay on the cuticle surface.
Proteins
Protein penetration depends upon their fragment size. Small fragment peptides and amino acids can get into the hair cortex.5 However, large proteins and their modified versions (e.g., silicone-modified wheat protein) stay at the hair’s surface.
The table below shows the difference between ingredients penetrating and remaining on the surface.
| Ingredient INCI | Can Penetrate | Stays at Surface |
|---|---|---|
| Sulfates | Yes | |
| Cetrimonium Chloride | Yes | |
| Behentrimonium Methosulfate / Chloride | Yes | |
| Cetyl Alcohol/Cetearyl Alcohol | Yes | |
| Aloe Vera Juice | Yes | Yes (certain components of juice can go inside) |
| Hydrolyzed Wheat Amino Acids (Silk, milk, wheat) | Yes | |
| Wheat Proteins | Yes | |
| Hydrolyzed Keratin | Yes | |
| Hydrolyzed Vegetable Protein | Yes | |
| Silk Amino acids | Yes | |
| Hydrolyzed Collagen | Yes | Yes |
| (Cocodimonium Hydroxypropyl Silk Amino Acids | Yes | |
| Wheat Amino Acids | Yes |
How Long Should You Deep Condition Your Hair?
Most people leave the deep conditioner on their hair for extended periods, hoping this will allow for deeper penetration. But this is not necessarily the case. The diffusion of active molecules depends on the concentration gradient.
When you first apply the product, there are more active molecules (concentration) outside the hair (hair surface), while the amount (concentration) inside the hair is zero. This is called a concentration gradient.
The active molecules have a more natural propensity to diffuse into the hair and achieve chemical balance (equilibrium). The precise time required to achieve this balance varies depending on each hair type.
The general understanding is that it needs 5-10 minutes. On wet hair, the presence of water helps diffusion, and consequently, this time frame is enough for the active ingredients to diffuse and reach a balance point.
Considering the above explanation, it is also important to consider the instructions on each product label. Some products may require 10 minutes, while others work better if left for 20 minutes. Your hair needs, the product, and the diffusion process should all be honored.
Can You Leave Deep Conditioner Overnight?
I personally know of multiple people who leave deep conditioners for much longer than stipulated. Sometimes they apply a 10-minute treatment for 30 minutes. But are there any extra benefits of leaving a deep conditioning treatment on longer?
Remember that an excess of anything in life can have adverse effects. This also applies to hair care products, as beneficial as they are. Once the molecules reach the equilibrium balance point, there is no way to force more molecules to diffuse into the hair. Once it’s in, it’s in.
Leaving the product on for a long time may negatively impact the hair and scalp. It may cause scalp discomfort, and the product may start drying up, causing scales on the hair shaft and scalp surface. The safest and most viable recommendation is to leave the product on for 5-10 minutes only.
Remember, I’m just presenting the science here. As always, let your hair be your guide! You know your hair better than anyone!
Many naturals condition their hair for hours at a time because they like the softness it develops. If you are in this group, you probably like over-conditioned hair. The softness you feel is most likely related to the change in the keratin, and you should be careful when handling your hair when it is that soft, as it will be weaker until it has time to recover its stronger conformation.
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Summary
Deep conditioning hair is not an exact science because it depends on the hair type, the state of the cuticle, and a range of other variables. We hope the information in this article will help you make informed decisions when deep conditioning your hair.
References
1. Ruetsch, S.; Kamath, Y.; Rele, A. S., Secondary ion mass spectrometric investigation of penetration of coconut and mineral oils into human hair. J. Cosmet. Sci 2001, 52, 169-184.
2. Gode, V.; Bhalla, N.; Shirhatti, V.; Mhaskar, S.; Kamath, Y., Quantitative measurement of the penetration of coconut oil into human hair using radiolabeled coconut oil. J Cosmet Sci 2012, 63 (1), 27-31.
3. Zviak, C., The Science of Hair Care. Taylor & Francis: 2005.
4. Schueller, R.; Romanowski, P., Conditioning Agents for Hair and Skin. Taylor & Francis: 1999.
5. Malinauskyte, E.; Shrestha, R.; Cornwell, P.; Gourion‐Arsiquaud, S.; Hindley, M., Penetration of different molecular weight hydrolysed keratins into hair fibres and their effects on the physical properties of textured hair. Inter. J. of Cosmet. Sci 2021, 43 (1), 26-37.
