|It's my brain that loves you (source)|
So what does the MHC have to do with your love life?
Well the most popular theory goes as such: If you want to have a healthy baby, you want to give it a varied MHC, therefore you want to find a man who has an MHC that is very different from your own.
And... Maybe you can detect whether a man has a MHC that is the same or different from yours through smell (maybe vision too). In 2005, a paper came out explaining that the Major Histocompatibility Complex (MHC) can be detected through smell, and (importantly) that women prefer the smell of men who have an MHC that is different from their own. (However another paper in 2008, did not replicate this preference)
|Possible new fragrance?|
|Roberts et al. 2008 Figure 2C: Odor desirability ratings.|
So my question is, why are the non-pill and pill users so different to begin with? Unless I am completely misunderstanding this graph, I would think the white bars should be similar, as they represent 'women who are not on birth control.' The huge difference between groups before the 'experimental treatment' should be a red flag: Something is already different between these women.
However, the pill session 1 (white) and pill session 2 (gray) bars are indeed different, and that is their 'main result.' Basically, women on the pill had an overall slight odor preference for MHC similar men, and the same women not on the pill had an odor preference for MHC dissimilar men.
So should you worry this Valentine's Day? Should you break up with your boyfriend because you were on birth control when you met? Should you spend a lot of time smelling your boyfriend's worn shirts analyzing how 'desirable' a scent the give off?
Probably not (unless you really like smelling sweaty shirts). There is more to relationship compatibility than histocompatibility, and making life-changing decisions based on possible olfactory disruptions due to birth control is just not a good idea.
Though if you are worried, you can read more about it at:
Context and Variation "will the pill mess up my ability to detect my one true love?"
First Nerve "pill goggles"
Roberts SC, Gosling LM, Carter V, & Petrie M (2008). MHC-correlated odour preferences in humans and the use of oral contraceptives. Proceedings. Biological sciences / The Royal Society, 275 (1652), 2715-22 PMID: 18700206