Scent reaches memory faster than any other sense. A smell can return you to a room you had forgotten, and to how you felt standing in it.

You will know this already. The coat of someone who has died, kept for the way it still holds them. Cut grass, and a summer with nothing to do in it. Open a child's box of crayons and a particular desk comes back, and the person who sat beside you at it.

"Smell is a potent wizard that transports you across thousands of miles and all the years you have lived. The odours of fruits waft me to my southern home, to my childhood frolics in the peach orchard. Other odours, instantaneous and fleeting, cause my heart to dilate joyously or contract with remembered grief."

Helen Keller

The science behind it

Smell is the oldest of the senses, and the first to form. The nose takes shape early in the first trimester. By nine weeks the receptors that detect smell are in place. By thirteen weeks they are wired to the brain. A newborn finds the breast by scent before it can focus its eyes.

The reason scent moves us is anatomical. The psychologist and neuroscientist Dr Rachel Herz has written that the brain's smell centre came first, and the amygdala, where emotion is processed, grew out of it. Put plainly: the part of the brain that reads smell and the part that feels are neighbours, and always have been.

The olfactory system connects straight to the limbic system, the seat of emotion and memory. That short wiring is why one breath of a familiar smell can bring back a whole scene.

How scent and memory work together

Breathe in, and receptors in the nose catch the scent molecules and send a signal to the olfactory bulb, at the base of the brain. From there it travels to the limbic system: to the amygdala, which handles emotion, and the hippocampus, which lays down memory. The line between a smell and both of those is direct. Little sits in between.

How a familiar scent brings a memory back

Meet a smell and the brain checks it against the ones it holds. When it finds a match, the memory returns, and the feeling attached to it returns with it. Baking brings back a grandmother's kitchen. A perfume brings back the person who wore it. The scent is the trigger. The feeling is what it carries.

Why scent is different from the other senses

Touch, taste, sight and sound are routed first through the thalamus and the thinking part of the brain. Smell is not. It goes straight to the amygdala and the hippocampus, ahead of conscious thought. That is why a smell can move you before you have named it.

Using scent to keep a moment

You can do this on purpose. Choose one scent for an occasion, use it only then, and the two bind together. Diffuse a blend on a particular trip and, months later, the same blend returns you to it. A few ways to try it:

• A scent made for a wedding day, worn only that day.
• One blend kept for a certain journey or place.
• The same oil brought out each year on a birthday.

Scent and habit

Scent also learns by repetition. Pair a smell with the same act often enough and the smell begins to prompt the act. This is how a calming oil earns its place: lavender, roman chamomile or vetiver, used each night before sleep, comes to tell the body it is time to rest.

The oils that may support memory

Some oils appear to sharpen attention. Studies suggest rosemary can support memory and alertness, and peppermint can help with focus and clarity. Others work the long way round: lavender and frankincense ease a busy nervous system, and a calmer mind holds and recalls more than a strained one.

The scent of remembering

Scent has always been tied to memory. Shakespeare knew it, and gave Ophelia the line: "There's rosemary, that's for remembrance." The research is still catching up with what the nose has always done.

A note: this piece is for general interest and is not medical advice. For any medical concern, please speak to a professional.