All scent originates as a chemical. Without chemicals, our brain would not be able to perceive, or "read" a scent. All around us are currents of air which are in constant motion. These currents contain myriads of complex combinations of odours that only trigger our attention when they irritate or please us.

Every time we breathe, our noses take in these chemicals, which pass over two small patch-like areas the size of a penny that contains five to six million tiny yellow receptor cells called the olfactory epithelium. Located on these receptor cells are microscopic filaments called cilia that extend into a watery mucous that surrounds the epithelium. On the cilia are proteins that respond to specific molecules. Like a key in a lock, when these proteins come into contact with its corresponding odorant molecule, a series of biological interactions are initiated.

First, there is an immediate rush of electrical activity as one experiences the perception of an odour. Our sensory nerves have long filaments, or axons, that are located on the opposite end of our olfactory nerves. The axons send messages to nerves located in the olfactory bulb which is shaped like a protracted balloon. The millions of axons that line its circumference transmit a pattern of activity that is specific to the individual cilia that come into contact with their corresponding molecules. Just as our brains are able to store and recognize complex notes from a symphony, it is also able to store and recognize complex combinations of fragrance notes that make up our favourite perfume.

How strong is our sense of smell?

Compared to a dog that has two hundred twenty million olfactory sensors, humans have only five or six million. While it may seem that humans have been short-changed where noses are concerned, we still can nevertheless, recognize thousands of different scents. Though we may not have a piranha-sharp sense of smell, we can, for instance, detect some substances in dilutions of less than one part per several billion parts air.

How sharp is our sense of smell at birth?

Unlike our other senses, our sense of smell is fully mature at birth and is one of the first senses that newborns experience. Their sense of smell helps them to locate their mother and her source of food. Without this functioning sense, baby animals would not be able to locate their mothers' milk.

Studies indicate that a newborn can recognize his or her mother's nipple simply by its scent. In one study, mothers washed one of their breasts while leaving the other left unwashed. Over two-thirds of the babies tested chose the unwashed breast.

Research conducted by Dr. Ira Lott reveals that when a baby is introduced to a fragrance while being stroked—much like a mother would do while nursing—his or her ability to remember that scent is increased. The results of her study suggest a connection between a baby's sense of smell and the ability to learn at an early age. Dr. Lott suggests that touching a baby increases his or her ability to remember a scent and may help to explain why a newborn readily recognizes his or her mother by her scent.

Other studies suggest that babies are most responsive to body odours but by the age of three they essentially have the same odour likes and dislike as adults. Newborns subjected to pleasant odours reacted positively while those subjected to unpleasant odours responded with "screwed up faces." Studies within the womb reveal that foetuses react to fragrances introduced through their mother while newborns are able to recognize her scent in as little as forty-eight hours after their birth.

Children's sense of smell—their odour likes and dislikes—do not parallel those of adults until the onset of puberty. A study conducted in 1976 and repeated in 1994 indicates that nine-year olds apparently do not have sensitivity to certain musk odours. However, their ability to detect particular odours is the same as both adults and young adults.