There are various ways in which you can lose sense of smell. For instance, people can lose their sense of smell if they are allergic to something. These people can often regain it if the object they are allergic to is removed. In other people, events such as car accidents can cause a person to lose certain connections in their brains and stop being able to smell. It can sometimes come back after long period of time, but this usually depends on the type of accident the person was involved in.

It's still very controversial. We are not entirely sure whether 'the chemistry of love' even applies to humans. Even if we do send off pheromones, it might be hard to detect them under all the perfumes we use. Humans spend billions of pounds on aftershave and perfume each year.

Part of it might have been that pheromones were useful in the past when we didn't wash every day. It isn't clear whether by washing, we remove all these chemical cues. One of the main pheromone interactions is between men and women. No-one knows whether women are turned on by male pheromones or repulsed! Females may be repulsed at certain times of the month but attracted when it is particularly good to mate. Some research suggests that now many women are on the pill, they might be responding in a different way to pheromones, or even be desensitised.

One of the functions for the hair under our arms is to act as a wick. They soak up some of the smelly chemicals under our arms. These chemicals have been shown to influence the timing of the female menstrual cycle.

I've seen this once with a man who had funny stretch marks on his stomach. His wife was pregnant, and it seems he was showing sympathetic changes with the female body. We know women can affect other women, but the evidence that women can change men's behaviour is a bit controversial. It's certainly possible that the hormonal changes will affect the man, but we don't know if men can pick up the chemicals. Men and women are very different, so it's hard to see how such effects can happen. The answer is no-one really knows!