Dogs can detect cancer. According to a British study, dogs can be trained to detect the odour of cancer suffering patients, as their capacity to smell is 10 to 100,000 times finer than that of humans. Dogs can smell the abnormal rate of protein that sick people secrete in their urine. Moreover, according to a study in California with 12,000 subjects, by smelling breath samples, dogs can detect 99% of cases of lung cancer.

Dogs can be trained to sense drugs. Some people believe erroneously that these dogs are drugged. This would be cruel and unethical. Dogs that can detect explosives never ingested any! Dogs can develop the ability to detect illegal substances after a long training based on games. Step by step, product by product, the trainer and the dog play games to find substances until the odour becomes recorded in the animal’s olfactory memory.

Corsican researchers discovered that female blue tits decorate the crown of their nests with odourous plants like mint or lavender. They renew them as soon as the odour fades away. It is believed that aromatic plants protect the nestlings through their insecticidal, fungicidal and disinfectant qualities.

Certain male butterflies can detect pheromone molecules at a distance of 10 km – an odour signal of invitation that appears on the antennae of females during the mating period.

Polar bears can smell the odour of a seal hidden under 1.5 m of snow.

Certain fishes can detect substances in their area with concentrations as low as one millionth or one billionth of a gram per litre.

A shark can find the smell of blood at a distance of 65 km.

The burrowing instinct in the first hours of human life shows the strength of the sense of smell: the odour of milk secretions makes the baby look for his mother’s breast and leads him to it. After six days, a baby can distinguish his mother’s milk from another’s. A child from 20 to 36 months can recognize his mother’s sweater.

Adult humans can detect more than 10,000 odours. Children can distinguish them more than adults because olfactory structure deteriorates with age.

A laboratory study led by Patricia Wallace in 1977 showed that humans can identify, within 80%, the sex of another human from the odour of the hand. Female subjects seemed to be better at this than males.

The human nose is made up of from 10 to 20 million chemically sensitive neurons. The olfactory mucus covers only 2 cm2, but it contains about 10 million nerve cells for smell, capable of recording an incredible amount of information.

About 800,000 kinds of plants have been identified and only 40% have been studied so far. Only 10% of all plants are odouriferous.

About 200 kinds of useful oils can be bought, as well as 4,000 aromatic essences.

These essences can be divided into 7 olfactory families from which 45 perfumes can be obtained.

Our olfactory capacity is stronger in the morning. Sensitivity to odours can vary from one individual to another.

Women can smell better than men, and non-smokers can smell better than smokers.

The olfactory capacity of women is influenced by their sexual hormones. It increases during ovulation as well as during pregnancy. On the other hand, it diminishes during menstruation, end of pregnancy, and after menopause.

There’s a decrease in olfactory sensitivity and capacity to identify odours after 60.  More than half of people over 80 can’t smell very well and 25% of them can’t smell anything at all.

Some people have dysosmia, where they mistake one scent for another. With phantosmia they identify a scent that doesn’t exist. 

Anosmia is the loss, total or partial, of all olfactory capacity, often caused by a cranial trauma, destruction of the olfactory nerve, nasal infections (chronic rhinitis, polypus) or Alzheimer's Disease which makes it progressively impossible for the brain to identify odours.

Anosmiacs can’t sense certain dangers like the smell of something burning, gas or spoiled food and they must compensate with extra caution. It could be dangerous to inhale unknown substances, as some volatile chemicals like ammonia or certain solvents can destroy the olfactory mucus. Other substances can have long term effects on the sense of smell. It is therefore advisable not to try to discover unidentified matter by smell.