hair science & biology · hair science and biology your hair is composed of keratin, a strong...

HAIRSCIENCEANDBIOLOGY

Yourhairiscomposedofkeratin,astrongfibrousprotein,andisbuiltfromcellssimilartothoseofyourskin.Theaveragenumberofhairsonthehumanscalpis120,000,althoughblondestendtohavemoreandredheadsandbrunettesless.

Ahealthyhaircanstretchupto30%ofitslength,canabsorbitsweightinwaterandswellupto20%ofitsdiameter.Asinglescalphaircanholdaweightof100gandanaverageheadofhairtwistedtogethercansupport23tons.

HAIRFOLLICLES

Hairgrowsfromasinglefollicle-anindentationintheskin.Eachhairfolliclehasitsownblood,nerveandmusclesupply.You’rebornwithaspecificnumberoffollicles,whichcan’tbechanged,andthesizeofyourhairfollicledeterminesthethicknessofyourhairs.Theshapeofthefollicledetermineswhetheryourhairgrowsoutstraightorcurlyorwavy.Atthebaseofyourfollicle,lyingonthedermis(thedeeperlayerofyourskin),isthepapilla–thebulbofhairwheremostgrowthtakesplace.Thenervesandmusclessurroundingyourfolliclesgiveyourhairitstactileproperties,allowingyoutofeeltheslightestmovement.Itisthesemusclesthatcontractandgiveyou‘goosebumps’whenyou’recoldorthreatened.

Thebloodvesselsthatsurroundyourfolliclescarrythenourishmentyourhairneedstogrow.Thisisoneofthereasonswhyyourdietissovitalforhealthierhairgrowthandstrength.HAIRSTRUCTURE

Yourhairismadeupofmanydifferentlayersandstructures:

THEHAIRBULBThehairbulbisastructureofactivelygrowingcells,whicheventuallyproducehair.Cellscontinuallydivideinthelowerpartofthebulbandpushupwards,graduallyhardening.Whentheyreachtheupperpartofthebulbtheyarrangethemselvesintosixcylindricallayers.Thethreeinnerlayersbecomethehair–madeupofthecuticle,thecortexandthemedulla–althoughthemedullaisn’talwayspresentinhairswithathinnerdiameter.Theouterthreelayersbecometheliningofthefollicleandformtheinnerrootsheathandbasementmembrane,aroundwhichlieundifferentiatedcells.Specificcellsinthehairbulb,melanocytes,makethepigmentcalledmelaninthatgivesyourhairitscolour.HAIRSHAFTYourhairshaftisthepartofyourhairthatcanbeseenaboveyourscalp.Itismadeofaproteincalledkeratin,compactedandcementedtogether.Keratinisaremarkablystrongprotein,whichisveryresistanttowearandtear.Itisthesamematerialthatskin,feathers,claws,nailsandhoovesarecomposedof.

Keratinisasulphur-richprotein,with‘disulphide’bondsholdingtheproteinstrandstogether.Thisplaysanimportantroleinanychemicalprocesslikeperming,relaxingandstraightening,whichbreakdisulphidebondsandresetthemtoadifferentconfigurationtochangetheshapeofthehair.Yourhairshaftisalsomadeofhydrogenbonds,whichhelptogivehairitsflexibility.Theyareweakerandmorenumerousthandisulphidebondsandareeasilybrokenwiththeapplicationofwater–thisiswhatallowsyoutochangethenaturalshapeofyourhairwithtongsorstraighteningirons.

Yourhairshaftconsistsofthreelayers:

1-TheCuticleAprotectivelayercomposedofoverlappingcells,likefishscalesorrooftiles,butfacingdownwards.TheoutercuticleholdsyourhairinthehairfolliclebymeansofaVelcro-likebond.Italsominimizesthemovementofwater(moisture)inandoutoftheunderlyingcortex.However,chemicalprocessesandweatheringcanliftthecuticleanddisruptthisbalance.Whenhealthy,i.e.smoothandintact,youroutercuticlegivesyourhairshineandprotectstheinnerlayersfromdamage.2-TheCortexFormsyourhair’smainbulkandpigment(colour).Itconsistsoflongkeratinfilaments,whichareheldtogetherbydisulphideandhydrogenbonds.Thehealthofyourcortexdependslargelyontheintegrityofthecuticleprotectingit.3-TheMedullaAthincoreoftransparentcellsandairspaces.HAIRGROWTHCYCLEItisusefultounderstandthehairgrowthcycleinordertorecogniseandunderstandmanyofthe

problemsyoucanencounterwithyourhair.Thehairgrowthcycleconsistsofthreedistinctstages–anagen,catagenandtelogen.ANAGENPHASE

Yourhairgrowsaroundhalfaninchamonth,andfasterinsummerthaninwinter.Thegrowthphase,oranagenphase,lastsanaverageof3-5years,soafull-lengthhairaverages18to30inches.TheanagenphaseisgenerallylongerinAsianhair,andcanlastaslongas7years,withhairbeingabletogrowuptoametre.CATAGENPHASEAttheendoftheanagenphase,yourhairentersthecatagenphase–ashorttransitionalphasethatlastsapproximately10days.TELOGENPHASELastlyyourhairentersthetelogenphase,arestingphasewhenyourhairisreleasedandfallsout.Thefolliclethenremainsinactivefor3monthsandthentheprocessisrepeated.Eachhairfollicleisindependentandgoesthroughthegrowthcycleatdifferenttimes,otherwiseallyourhairwouldfalloutatonce.Instead,youonlyshedacertainnumberofhairsaday–upto80hairsonahealthyheadofhair.Hairloss,hairthinningandproblemswithhairgrowthoccurwhenthegrowthcycleisdisrupted.Thiscanbetriggeredbyconditionssuchasnutritionalandmedicalissues,illnessorstress.Forinstance,sixweeksafterintensivedietingorahealthissueyoucanexperiencetelogeneffluvium(diffusehairfall).Thisoccurswhenyouranagenphaseiscutshortandmanyhairsenterthetelogenphaseatthesametime.Ifyourhairgrowthcycleisconstantlychallenged,youmayfindyourhairwillnotgrowaslongasitpreviouslyusedto.Thisisbecauseyourhairsareneverallowedtostayintheanagen(growing)phaselongenoughforyourhairstoreachthedesiredlength.