The Trichological Society-Straightening-Relaxing hair

Hairdressing Sciences

One of a series of articles in which Mr D Dane FTTS MAE FRMS
(a Clinical Trichologist, Microscopist, Fellow and Past President of The Trichological Society)
addresses scientific and practical issues associated with certain hairdressing procedures:

STRAIGHTENING and RELAXING - the chemistry and nature of these processes to hair and skin.

All hair-straightening chemicals are active and are inherently dangerous in that they are designed to alter the structure of hair ( hard keratin). It is quite possible by using proper skills care and attention, and particularly by keeping strictly to the product manufacturer's recommendations guidelines or instructions, for an ordinarily competent practitioner to avoid processing hair to a point where the hair chemistry might suffer sufficient damage for it to lead to loss of condition and structural strength and suffer subsequent breakage. This also applies to the skin of the scalp or other nearby skin tissues ( soft keratin). The living tissue under the surface should never be put to irritation or be in any way inflamed by the chemicals. For that reason lotions or creams should always be applied with utmost care away from the skin - and then never allowed to come into direct skin or scalp contact. Chemical burns would most likely result due to the high alkalinity and reactiveness of straighteners and particularly of relaxers. The manufacturer's instructions re processing-time, and a continuous careful checking throughout this period of both lotions/creams and neutraliser, should be carefully adhered-to.

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It should be recognised and is industry-accepted that any chemical process administered to the hair will weaken it to some extent, and it is initially for the manufacturer of the product being used but then for the product user to minimise such damage as much as possible to within an acceptable degree. This means keeping close records of past treatments, especially noting any past treatments of a new client remembering that hairs only grow 12cm-13cm per year, and always paying attention to the history of any hairlengths before carrying out any proposed treatment. If seen as a 'percentage' of damage upon a hair that was one-time virgin, each chemical application and processing will add a further percentage of damage or weakness to that hairshaft. The hair's feel or look , even its apparent elasticity is not a precise indicator of that head of hair's porosity. Such porosity will naturally vary down its length, and porosity (an indicator of hair's internal and external structural breakdown) can often later be linked to hairshaft damage sufficient to produce breakage which might not otherwise have occurred.

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Even virgin hair that has been subjected to Straightening or Relaxing chemicals at a heightened temperature or for too long (and in these matters even 1 minute over recommended time can be too long since natural scalp-temperature will have risen during processing, and chemical activity will also have raised hair temperature) will lose its structural strength and become dry and brittle. After such processing the later-dressed hair will not hold its shape. It may appear limp or frizzy and will be unruly. Such hair is known as 'over-processed' . Breakage may then easily follow as the hair undergoes any normal daily wear. Hair that is unknown by the hairdresser from previous experience of treatment to that client poses special risk, and hair tests using the proposed chemical product must have been made before any work is undertaken, the results then gauged carefully by the hairdresser as to the wisdom of proceeding without likelihood of damage. To ensure safety manufacturers instruct that hair tests be carried out prior to each and every application. If the skin of the scalp has in any way become involved by direct chemical contact, whether during application or within acceptable processing-time, it will usually first become red and inflamed and be accompanied by burning or sensations of irritation. Chemical burns may then quickly develop. Dependent on the severity of the processing blisters or open sores may then develop which will later dry as scabs. Even after mild processing with skin contact or sensitisation, as the skin heals intense itching of the skin/scalp will be experienced. Infection is immediately always likely since it is usual for scratching to occur at some point during the days/weeks of the healing process. The skin surface will usually flake off often heavily for a long period before healing is complete. This can thereafter lead to a scaling condition that may become chronic.

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The Chemistry involved : The term used and the request made by the public for 'straightening' is very often misunderstood and in the current climate of 'smoothing' hair it is vital that a competent hairdresser appreciates the chemical difference between 'straightening' and 'relaxing' not only for reasons of compatibility as will be seen, but also for client safety - of both hair and skin. Skin is made up from amino acids in the body to form protein molecules called soft keratin . Hair is made up from amino acids in the body to form large long-chain protein molecules called hard keratin . The difference lies mainly in that hair contains more sulphur atoms than skin. In considering hair keratin - this elastic and naturally durable substance is itself composed of long spiral chains called polypeptides each of which have two sulphur atoms ( disulphide bonds ) that create bridges between the chains. These sulphur bridges are therefore part of the bonds holding the polypeptide chains together. The bond is an amino acid in its own right, called cystine .

'Straightener' - sometimes referred to as 'Straight Perm' or Afro 'Curly-Perm' : This term is only used correctly when the active chemical thioglycollate (also used for cold permanent waving) is put on and absorbed into the hair. Using this chemical the sulphur bridges of cystine -bonds break down and hydrogen atoms are fixed in place. This is a reduction reaction. The result is a softening of the hair. This enables it to be either bent or straightened because new molecules of another amino acid cysteine are then formed in some of the positions that were previously cystine . By joining-up the broken sulphur bridges by removing the hydrogen atoms in these new temporary cysteine -bonds, the sulphur atoms come together again to reform cystine as they were formerly, but the hair having now changed its shape if it had been bent or straightened. This removal of hydrogen is an oxidation reaction, having required an oxidising agent to be put into the hair. This was the 'neutraliser'.

[ In this latter reaction the oxygen atoms from the neutraliser will be moved into the hair-keratin molecule where they join-up with the hydrogens and form a water molecule. The remaining sulphur atoms are now able to come together, then re forming the sulphur bonds as cystine again in their new positions of bentness or straightness.]

A hair 'straightener' therefore depends upon the processes of reduction and oxidation - which uses the alkaline chemical thioglycollate to reduce , and an acid hydrogen peroxide or bromate neutraliser to oxidise and fix.

'Relaxer' : This term is only used corectly when the active chemistry of a hydroxide (whether of sodium, calcium or potassium) is put on and absorbed into the hair.
A 'relaxer' depends upon the process of hydrolysis . Whereas the moderately alkaline thioglycollate 'straightener' which has a pH of 9.2-9.5 simply breaks down only some sulphur bonds and is then set to rebuild them as whole sulphur bonds again, leaving them with great strength and allowing elasticity to remain between the polypeptide chains - the far stronger alkalinity of the hydroxide 'relaxer' which has a pH of 10-14 breaks down the sulphur bonds completely by chemical hydrolysis, able to reform them only as a weaker new type of bond, a lanthionine bond, which contains only one sulphur atom. This is a hydrolysis reaction - quite different from the reduction and oxidation reactions described above for a 'straightener'. An oxidising/acid form of neutraliser is still required and is usually built into a colour-signalling (alkali clearing) after-treatment shampoo for special use with the relaxer chemical, but importantly it must be noted that the resultant structure of any 'relaxed' hair is and will forever remain fixed and structurally altered in a way that can not be reversed , and will inherently be considerably weakened, much more so than if it had been 'straightened'. A hydrolysed lanthionine bond has much less strength than its forbear the sulphur (cystine) bond - and as explained, can never thereafter be altered. For this reason, previously thioglycollate-treated hairlengths (straightened) must never come into contact with hydroxide, and hydroxide-treated hairlengths (relaxed) must never be allowed to come into contact with thioglycollate - since total loss of structure, all elasticity and all hairstrength, must be an inevitable result.

NB : For avoidance of doubt therefore, pre-treatment hair tests on a cut sample in advance of either relaxer or straightener work is an absolute necessity for an unknown head of hair.