Sniffing out 5 things you didn't know about the human nose

What do our noses "know"? A lot, according to a recent study that reveals that the human nose can detect more than 1 trillion different smells.

The study, published in the journal Science, claims we can detect many more smells than the commonly agreed number of 10,000.

But wait, did you even know you could even make out 10,000 distinct scents in the first place? Here are five other things about your sense of smell that may surprise you.

1. Women's noses win

A woman's sense of smell is much stronger than a man's, and even more so in the first half of her menstrual cycle, reports the Daily Mirror. It reaches its peak when she is most fertile.

Want a keener sense of smell? There are ways to train those scent receptors, according to a Wall Street Journal report. Dr Alan Hirsch, director of the Smell & Taste Treatment & Research Foundation in Chicago, recommends something he calls "sniff therapy".

The article says: Choose three or four different types of scents that you find pleasant, for example a floral shampoo, fruity berries, or coffee, avoiding irritating scents like onion or ammonia, which can hamper smelling ability. Sniffing these scents frequently, around four to six times a day, will eventually spark different receptors in the nose to work.

2. Noses get bored easily

When entering a bakery or florist, you are very aware of the aromas around you. But by the time you leave, you will no longer be able to detect them, says the Sense of Smell Lab, which develops products that use our sense of smell to influence behaviour.

Our noses are like caves designed to moisten, channel and filter the air we breathe. When we breathe in, the air is cleaned by little hairs called cilia that work like a broom, sweeping out all the other things that entered the nose. The air then passes through a thick layer of mucous to the olfactory bulb near the front of the brain. This is where the odours are identified as each scent molecule fits perfectly into a nerve cell like a lock and key. These cells send signals along the olfactory nerve to the brain where they are identified.

3. Smell trumps sight at recall

People can remember smells with 65 per cent accuracy after a year, while visual recall is about 50 per cent after three months, reports the Daily Mirror. One of the most evocative smells from childhood is crayons, it says. 

The sense of smell is quite primitive and feeds into the emotional areas of the brain much more directly than our other senses. When you smell something favourable or unpleasant, that message is sent directly to your brain and into your limbic system, where feelings of pleasure and happiness are derived, writes the Sense of Smell Lab.

4. You have a unique "smellprint"

Like your fingerprint, how you smell is unique. No two people have the same smellprint, except for identical twins - and this unique scent is determined by factors including genes, the environment, and your diet. Medicines, your emotional state, skin type, and even the weather, all play a part in how you smell too, adds the Lab.

5. Our sense of smell declines as we age

Our sense of smell peaks when we are in our late teens and then begins to decline. People who have an impaired ability to smell, and therefore taste, tend to follow diets that are less healthy. Losing your sense of smell, a condition called anosmia, can be dangerous because you can't smell food that has gone bad, or even a gas leak. Treatment may be required for this condition.

Upper respiratory infections, pollution, head trauma and diseases such as diabetes may affect our sense of smell. Sometimes the problem is temporary, due to environmental factors such as cigarette smoke or chemical fumes, reports the WSJ.