Last Updated on April 10, 2023 by Verna Meachum

There is a lot of debate surrounding the topic of deep conditioning and whether or not it is necessary for everyone with curly hair.

Some people believe that this is a must-do step in order to keep your curls looking their best, while others say that it all depends on the type of hair you have.

But is deep conditioning necessary for everyone with curly hair? Or is it something that only people with certain types of curls need to do?

In this blog post, we will explore and discuss whether or not deep conditioning is necessary for every curly haired person, and we’ll also talk about how long you should deep condition and what ingredients you need to do it.

Deep Conditioning – A Highly Regarded Treatment for Curly Hair

Curlies favor deep conditioners, which are accessible in a range of deep conditioning treatments on the market.

We’ve been taught that deep conditioners are one of the most critical curls care steps, to deep condition once a week, and to leave it in for 20 – 30 minutes.

Deep conditioning hair is frequently advised by hairstylists and experts, especially for clients with brittle, damaged, or porous hair.

A general perception about a deep conditioning treatment is that it is a “more concentrated formulation”, it offers better “penetration of active ingredients” and it provides “superior hair quality in the end”.

There are several fundamental questions regarding “Deep Conditioning,” hair and we will attempt to help you understand the science behind it.

So, what is deep conditioning?

Deep conditioning treatments aim to penetrate certain active ingredients into the hair fibers.

The treatment is frequently applied on damaged hair fibers to restore their mechanical strength, improve hair quality, and ease their manageability.

Hair that has been damaged is highly porous, frizzy, and susceptible to break during daily combing, brushing, or styling. Chemical treatments such as bleaching, perms, or straightening may result in significant hair damage.

Prolonged and repeated exposure to sunlight also damages hair fibers. Hair loses its proteins and becomes weak. Microscopic examinations of the hair surface reveal cracks along the hair shaft as well as deep inside the hair cortex structure.

In this instance, deep conditioning treatments are vital to restore hair quality and improve its overall health. It is a good way to restore and recover the hair’s mechanical strength.

Is deep conditioning a myth?

Nope, it is not a myth.

Deep conditioning is a scientific topic and there are clear shreds of evidence supporting the penetration of active molecules.

Various reports have examined the mechanism of deep conditioning and how active ingredients work inside the hair fiber.^1-2

Scientists have worked out the possible mechanism of hair conditioning, describing how different hair conditioning agents interact with hair cuticles, and can even penetrate hair fiber.

Can you actually “deep” condition your hair?

Cuticles are the first point of interaction for hair conditioning agents.

During this initial interaction, most of the conditioning ingredients stick to the hair surface and do not penetrate.

Cationic surfactants and polymers are the most common types of 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-sized conditioning molecules can pass through the cuticle openings and penetrate 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 such molecules which can penetrate hair fibers.

A tentative list of these ingredients has been provided at the end of this article.

How long should you deep condition?

Most people leave deep conditioner on their hair for an extended period of time in the hope that this will allow for deeper penetration.

However, this may not be the case. The diffusion of active molecules depends upon the concentration gradient.

When you first apply the product, there are more active molecules (concentration) outside 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.

Is it harmful to leave it on overnight?

Are there any extra benefits of leaving a deep conditioning treatment on for a longer period (let’s say instead of 5 minutes, but 30 minutes)?

EXCESS of anything is bad. 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.

There are exceptions to every rule, however, leaving the product for a long time on hair and scalp may have a negative impact.

It may cause scalp discomfort, the product may start drying up leaving scales on the hair shaft and scalp surface.

So, the bottom line, leave the product on for 5-10 minutes only. I’m just presenting the science here, so don’t hate me later.

As always, let your hair be your guide! You know your hair better than anyone!

There are many naturals who will condition their hair for hours at a time because they like the softness that it develops. If you are in this group, you are someone who likes over-conditioned hair. The softness you are feeling 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. 

The Natural Haven Bloom

Molecular Size and Shape of the Active Molecule

Cuticles pores are very small. The microscopic examination reveal that only the molecules of a certain 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 adsorption is known to help pore opening and thus boost active ingredient diffusion.

These conditioning molecules pass through the cuticle layers and finally end up inside the cortex.

Chemically treated and damaged hair fibers have wider cuticle pore size and so it becomes easier for molecules to diffuse through.

What ingredients can diffuse?

As previously said, the diffusion ability of a substance is determined by its molecular size and shape.

Large molecules with greater positive charge stick the cuticle layers and therefore are unable to penetrate the hair.

However, smaller and 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, an empirical list is created.

Surfactants

Anionic surfactants, such as sodium lauryl sulfate or sodium laureth sulfate, carry a negative charge and are effective to clean hair.

Most of these ingredients are water-soluble and they mostly stay outside, and being anionic are easy to rinse off.

However, one should remember, sulfates are harsh chemicals and may strip off essential lipids from the hair surface, leaving 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 negative amino acid sites at the hair shaft.

Most of the cationics found in market formulations are large molecules in size and carry large positive charge density; that’s why they stay on the cuticle surface.

Proteins

Here again, 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 surface of the hair.

Conclusion

We hope that this deep conditioning article has been of some help.

Conditioning hair is not an exact science because it depends on the hair type, the condition of the cuticle, and a range of other variables.

However, the information presented in this article should at least help you to make an informed decision when deep conditioning your hair.

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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.