The 10 primary smells perceived by the human sense of smell

There are 10 primary types of smells: fruity, citrus, floral, minty, sweet, smoky, woody or resinous, chemical, pungent and rotten. This is the classification proposed by a study published in the scientific journal PLOS One and, although the human sense of smell picks up far more nuances, almost every smell you come across in daily life fits into one of these ten categories or a blend of several. Below you will find each one with everyday examples, which smells we find pleasant and which we don't, where the idea of the 7 primary odours comes from and how all of this translates into the olfactory families of perfume.

What primary smells are and how we perceive them

Smell works in combinations. Our nose has around 400 types of olfactory receptors, and each aromatic molecule activates several of them at once, with different intensity. The brain reads that combination like a code and interprets it as "lemon" or "smoke". That is why primary smells don't work like primary colours: there are no three or four basic smells that, mixed together, create all the others.

What does exist are categories that help us sort what we smell. The researchers behind the PLOS One study started from an atlas of about 150 odorous substances, described by hundreds of people using a vocabulary of almost 150 terms ("sweet", "woody", "rotten"…), and looked for the descriptions that kept appearing together. The result was 10 groups that sum up very well the way we talk about smells.

The 10 types of smells, with examples

For each type of smell you have easy-to-recognise examples and, where it makes sense, the perfume family it usually appears in. If you are looking for 10 examples of the sense of smell for a class or to train your nose, this list works as it is.

1. Fruity

The scent of fruit, except citrus, which has its own group. Think of a freshly cut apple, a ripe peach, a pear or a handful of red berries. In perfumery it is the basis of the fruity family and brings juicy, cheerful notes, very common in women's and summer fragrances.

2. Citrus

Lemon, orange, mandarin, grapefruit and lime. These smells are fresh, sparkling and very easy to identify; in the original study this category is linked above all to lemon. It is the opening note of the citrus family and of many fresh colognes: the first thing you notice when you spray and the first thing to fade.

3. Floral

Rose, jasmine, orange blossom, lavender or iris. In the study this category is called "fragrant", because it brings together the smells we associate with something perfumed and pleasant, and flowers are its clearest example. It is the heart of perfumery: the floral family is the largest, and almost every fragrance contains a flower somewhere in its composition.

4. Minty or refreshing

Mint, spearmint, eucalyptus, toothpaste or a mint sweet. They create a cold sensation in the nose even though the temperature does not change. In perfume it appears in aromatic and fougère fragrances, alongside lavender, rosemary or basil, especially in men's perfumes.

5. Sweet

Rich, warm and creamy: vanilla, chocolate, caramel, honey, a cake fresh out of the oven or candyfloss at the fair. It is one of the most universally loved smells. In perfumery it defines the gourmand family and adds warmth to many oriental perfumes.

6. Smoky or toasted

Wood smoke, roasted coffee, toast or popcorn. In the PLOS One study this category is described precisely with popcorn: a smell of hot, toasted, slightly buttery grain. In perfume you find its smoky side in notes such as birch, incense or tobacco, present in intense woody and oriental fragrances.

7. Woody or resinous

A freshly sharpened pencil, the inside of a cedar wardrobe, a pine forest after the rain, tree bark or resin dripping down a trunk. These smells are dry, warm and full-bodied. In perfumery they make up the woody family, with notes of cedar, sandalwood, vetiver or patchouli, and they usually sit at the base of the fragrance because they last a long time on the skin.

8. Chemical

Alcohol, ammonia, bleach, petrol, nail polish remover or fresh paint. These are synthetic smells we link with cleaning, industry or solvents. They don't form a perfume family, although some modern fragrances play with metallic or mineral nuances that faintly recall this category.

9. Pungent or acrid

Harsh smells that almost sting your nose: garlic, raw onion, a freshly struck match, vinegar or a very mature cheese. If you are looking for examples of an acrid smell, vinegar and a struck match are the clearest. It isn't used as such in perfumery, although spices like black pepper or clove share that sharp edge and give character to the spicy family.

10. Rotten or sickening

Unpleasant and penetrating: spoiled meat, rotten eggs, rubbish or stagnant water. It is the smell that warns us something should not be eaten. It has no place in a perfume, although tiny doses of certain raw materials with an animalic background help a flower like jasmine feel fleshier and more real.

Pleasant and unpleasant smells

Whether we like a smell or not depends partly on biology and partly on experience. Sweet, floral, citrus and fruity smells tend to please almost everyone, while rotten and pungent ones cause rejection because the brain links them to danger: spoiled food, gases or toxic substances.

Some of the most frequently mentioned pleasant smells:

• Freshly baked bread and coffee.
• Vanilla and chocolate.
• Clean laundry and soap.
• Wet earth after the rain.
• Freshly cut grass.
• Fresh flowers, such as rose or orange blossom.

And some of the most common unpleasant smells:

• Decomposing food and rubbish.
• Rotten eggs.
• Stale tobacco smoke.
• Stale sweat.
• Strong chemicals, such as ammonia.

Culture and memories weigh a lot. The smell of petrol, wax or a strong cheese can delight one person and disgust another, and a scent tied to a happy moment can become your favourite even if, objectively, there is nothing special about it.

What about the 7 primary odours?

Before the 10-category classification, the best-known theory was that of the 7 primary odours, proposed by the British biochemist John Amoore. His idea, called the stereochemical theory, was that odour molecules fit into the receptors in the nose like a key in a lock, and that their shape determines the smell we perceive. According to Amoore, all smells would be combinations of seven basic ones:

• Camphoraceous: like camphor or mothballs.
• Musky: warm, animalic and enveloping, like musk.
• Floral: like rose or jasmine.
• Pepperminty: like mint.
• Ethereal: light and volatile, like ether or some cleaning fluids.
• Pungent: like vinegar.
• Putrid: like rotten eggs.

The difference from the PLOS One classification lies in the method. Amoore put forward a hypothesis about how receptors work: five of his odours would depend on the shape of the molecule and the other two, pungent and putrid, on its electrical charge. The 10-category study doesn't try to explain the mechanism; instead, it analyses how people describe real smells and groups those descriptions statistically. Today we know smell is more complex than a lock with seven shapes, but Amoore's list is still a good reference for understanding where the idea of a "primary odour" comes from.

From primary smells to the olfactory families of perfume

Primary smells describe what we perceive; olfactory families organise perfumes. One of the best-known classifications is Michael Edwards' fragrance wheel, which starts from four large families (floral, fresh, woody and oriental) and keeps subdividing them. In everyday perfumery, these are the families people work with:

• Citrus: bergamot, lemon, mandarin and grapefruit. Bright, fresh perfumes, perfect for hot weather. Guide to citrus perfumes · Shop citrus perfumes
• Floral: rose, jasmine, orange blossom and peony. The largest family, from romantic bouquets to the most intense white flowers. Guide to floral perfumes · Shop floral perfumes
• Woody: cedar, sandalwood, vetiver and patchouli. Elegant, dry and very long-lasting on the skin. Guide to woody perfumes · Shop woody perfumes
• Oriental: amber, vanilla, spices and resins. Warm, sensual and intense, ideal for evenings and winter. Guide to oriental perfumes · Shop oriental perfumes
• Aquatic: marine and ozonic notes that recall the sea and the open air. A clean, light freshness. Guide to aquatic perfumes · Shop aquatic perfumes
• Spicy: pepper, cinnamon, cardamom and clove. It brings warmth and character, and connects directly with pungent smells. Guide to spicy perfumes · Shop spicy perfumes
• Fougère or aromatic: lavender, geranium, oakmoss and coumarin. The classic structure of men's perfumery, with the minty freshness of aromatic herbs. Guide to fougère perfumes · Shop fougère perfumes
• Chypre: bergamot in the opening, rose or jasmine in the heart and oakmoss and patchouli in the base. Sophisticated and full of character. Guide to chypre perfumes · Shop chypre perfumes
• Gourmand: vanilla, caramel, chocolate and praline. The sweet smell turned into perfume. Guide to gourmand perfumes · Shop gourmand perfumes
• Fruity: peach, red berries, pear and apple. Cheerful, juicy and carefree. Shop fruity perfumes

If you have never been sure which family you like, think about the everyday smells you enjoy most. If you love the smell of a freshly peeled orange, start with citrus; if vanilla is your weakness, try gourmand and oriental perfumes; and if the forest is your thing, go for woody scents.

Frequently asked questions about primary smells

How many different smells can the human nose distinguish?

One of the most widely cited studies estimated that the human sense of smell could distinguish more than a trillion different odours, although in practice we can only name a small fraction of them. The PLOS One study grouped all those scents into 10 primary categories.

Why do smells trigger memories so intensely?

The olfactory bulb is directly connected to the amygdala and the hippocampus, the brain regions linked to emotion and memory. Unlike the other senses, smell does not pass through the thalamus first, which is why a scent can bring back a very vivid memory instantly.

What is the relationship between primary smells and the olfactory families of perfumery?

Olfactory families (citrus, floral, woody, oriental, fougère, chypre, gourmand…) group perfumes according to their dominant notes. They overlap with primary smells, but they reflect a creative and commercial perspective, while the 10 primary smells are a scientific classification based on how we perceive and describe scents.

What are the most pleasant smells for humans?

Sweet smells like vanilla or chocolate, florals like rose or orange blossom, citrus and scents linked to home, such as freshly baked bread, coffee or clean laundry, are the most liked in almost every culture. Even so, liking a smell depends a great deal on each person's experiences and memories.

How many types of smells are there?

According to the study published in PLOS One, there are 10 types of primary smells: fruity, citrus, floral, minty, sweet, smoky, woody, chemical, pungent and rotten. John Amoore's classic theory spoke of 7 primary odours: camphoraceous, musky, floral, pepperminty, ethereal, pungent and putrid.