Of the five ma­jor sens­es, see­ing, hear­ing, touch­ing, tast­ing and smelling, the last, un­less you are a wine con­nois­seur, must be the least ap­pre­ci­at­ed. As any­one with a cold knows, tast­ing is re­lat­ed to smelling. In fact, all the sens­es do this; they col­lab­o­rate with each oth­er. The use of all the sens­es to­geth­er, see­ing a loved per­son, hear­ing their voice, touch­ing their lips, tast­ing their skin and above all, smelling them, is guar­an­teed to bring a smile to the face of the most frus­trat­ed hu­man.

How­ev­er, hu­mans do re­ly most heav­i­ly on vi­su­al de­scrip­tions and con­sid­er sight the most crit­i­cal for day-to-day mo­bil­i­ty and qual­i­ty of life.

While sight is con­sid­ered our most dom­i­nant and val­ued sense for gath­er­ing in­for­ma­tion, the sense of smell is sci­en­tif­i­cal­ly con­sid­ered the most pow­er­ful and emo­tion­al­ly evoca­tive hu­man sense. This is be­cause the nerves in the nose have di­rect ac­cess to the brain.

Un­like oth­er sens­es, they do not have to go through var­i­ous sen­so­ry parts of the brain be­fore be­ing processed. Smell sig­nals go straight to the ol­fac­to­ry bulb, the part of the brain that lies at the bot­tom of the front of the brain, just be­hind the nose, that process­es ol­fac­to­ry in­for­ma­tion.

The ol­fac­to­ry bulb in turn has an im­me­di­ate phys­i­cal con­nec­tion to the amyg­dala and the hip­pocam­pus—the brain’s emo­tion­al and mem­o­ry cen­tres. Be­cause of this unique wiring, scents can trig­ger vivid emo­tion­al mem­o­ries and be­hav­iour­al re­spons­es faster and more in­tense­ly than sights, sounds or even touch.

It is no sur­prise then that the sense of smell shapes hu­man re­la­tion­ships and the smell of a per­son is said to be ei­ther one of the most at­trac­tive or un­at­trac­tive char­ac­ter­is­tics of hu­mans.

We know, for ex­am­ple, that we are nat­u­ral­ly drawn to the scent of in­di­vid­u­als with dif­fer­ent ma­jor his­to­com­pat­i­bil­i­ty com­plex (MHC) genes to ours. This helps to pre­vent in­breed­ing, and the com­bi­na­tion of dif­fer­ent MHC pro­files re­sults in health­i­er, more ge­net­i­cal­ly di­verse off­spring. It’s rather like the be­lief that chil­dren from dif­fer­ent eth­nic par­ents are health­i­er than if they come from sim­i­lar ge­net­ic back­grounds. So far, the sci­en­tif­ic ev­i­dence for this is lack­ing. Greater ge­net­ic dis­tance be­tween par­ents is as­so­ci­at­ed with slight in­creas­es in adult height, lung ca­pac­i­ty and cog­ni­tive test scores, but no sig­nif­i­cant link has yet been found be­tween di­verse parental back­grounds and ma­jor chron­ic dis­ease.

We al­so know that body odour ranks high­er than vi­su­al ap­pear­ance when peo­ple eval­u­ate po­ten­tial long-term ro­man­tic part­ners. At this point, the pen­ny might drop for some peo­ple - an “AHA!” mo­ment.

All of this helps ex­plain those sob­by mo­ments in films when the ma­cho hero, while pack­ing away his dead lover’s lin­gerie, sud­den­ly stops, puts the gar­ment to his nose, smells and pass­es out.

Yes, there is some truth to this.

It al­so ex­plains why peo­ple with con­gen­i­tal or ac­quired anos­mia (the in­abil­i­ty to smell) of­ten re­port low­er re­la­tion­ship se­cu­ri­ty, in­ti­ma­cy is­sues and dif­fi­cul­ty form­ing ini­tial ro­man­tic con­nec­tions. In par­tic­u­lar, men with the con­di­tion re­port hav­ing few­er life­time sex­u­al part­ners com­pared to men whose abil­i­ty to smell is in­tact.

All this is a set-up to my main point. Ba­bies’ smell! Or the smell of ba­bies.

Ba­bies smell won­der­ful­ly to their par­ents. Their teenagers do not! In­fant body odour al­ways smells pleas­ant­ly, and that smell seems to ac­ti­vate plea­sure and re­ward cen­tres in the brain of adults that may be es­sen­tial to a ba­by’s sur­vival.

Par­ents gen­er­al­ly show a strong pos­i­tive re­sponse to the gen­er­al scent of in­fants. Par­ents can specif­i­cal­ly dis­tin­guish and in­tense­ly favour the unique scent of their own ba­by over the scent of oth­er ba­bies. We have al­ways known that moth­ers can recog­nise the cry of their new­born soon af­ter giv­ing birth. We now know that they can do the same thing with smell with­in a cou­ple of days. The im­me­di­ate dri­ve to pro­tect, nur­ture and care for a spe­cif­ic child has im­mense sur­vival and evo­lu­tion­ary ad­van­tages, of course.

Al­though it hap­pens a bit more slow­ly, fa­thers can iden­ti­fy their own chil­dren by body odour just as ac­cu­rate­ly as moth­ers and find it just as pleas­ant.

The ques­tion is whether this at­trac­tive­ness com­pen­sates for the prob­lems as­so­ci­at­ed with bring­ing up chil­dren. The mod­ern trend to­wards hav­ing no chil­dren may be an­swer­ing this ques­tion.

The oth­er in­ter­est­ing thing is that odour pleas­ant­ness di­min­ish­es as the child grows old­er. This is seen as an­tic­i­pa­to­ry prepa­ra­tion to­wards push­ing the ado­les­cent out of the home. Whether the teenag­er shares in the same ol­fac­to­ry feel­ings is not known.