1. It is damaging to cycle between raised and smooth cuticles (or open and closed)
Scientists have observed that when a lock of hair is cut and preserved in a jar, it simply does not suffer the same wear and tear that hair which is on your head suffers. This is because it avoids being washed and the subsequent swelling that can impact the cuticles and cause them to chip away. The strands also are not brushed or combed, again preserving the cuticle.
Raised hair cuticles are common in relaxed or bleached hair and are in part the reason why these processes can make hair more fragile and susceptible to damage (Journal of Cosmetic Dermatology, pp 180-185, 2003).
I would never regard a raised cuticle or 'open cuticle' as a positive. It is necessary and unavoidable for example you may need to wet your hair to moisturise it or you may use shampoo to cleanse your hair. Both of these actions do slightly swell and raise the hair cuticle . However, this is the reason why hair conditioner exists, to fix this problem (and it is a problem) of raised cuticles. This is also the reason why coconut oil as a prewash can help you have less damage.
2. The first action of hair conditioner is to smooth ('close') the cuticle.
Human hair naturally has a slight negative charge and this increases further when hair is shampooed as shampoo contains surfactants with a negative charge. This has the effect of raising the cuticle slightly. Hair conditioner immediately acts to counteract this because it contains positively charged (cationic) surfactants. This action happens rapidly within seconds.
Therefore, your hair will not be seating out there with raised cuticles waiting for substances to penetrate. Substances that can penetrate hair (see this post), do so because they have the right chemistry, i.e size, shape, charge and/or flexibility, to be able to get underneath the tiny space of a smooth cuticle. They do not require an 'open' cuticle to penetrate.
* As a general note for those who are new to the blog, I do not like to use the term open and closed cuticles although these are terms widely used in the natural hair world and I am certain many of you understand what they mean. The cuticle really does not open, what it does do is raise itself from the surface. In place of open and closed, I use the terms raised and smooth.
Conclusion: You do not need to and do not want to 'open' your hair cuticles by force. It is unavoidable if you wet your hair or use shampoo. Hair conditioner will 'close' the cuticles and protect the hair from damage. Using heat is beneficial not for increasing swelling of hair or 'opening' cuticles but rather for allowing more conditioner to stick on the surface of hair (aDsorb) - see this post
For advanced learners:
1. Technically not all shampoo will cause the cuticle to be raised. Shampoo with non-ionic or zwitterionic surfactants do not have this effect (Mild Shampoo list, In detail - charge and shampoo)
2. If you are wondering, here are examples of cationic sufactants found in hair conditioner: stearalkonium chloride, cetrimonium chloride, dicetyldimonium chloride, behentrimonium methosulfate, behentrimonium chloride, stearamidopropyl dimethylamine, etc.
Next Friday: Does penetration of an ingredient in hair conditioneractually make it more effective?