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A woman who was born without the brain regions required for smell has mysteriously started smelling things for the first time in her twenties and finds it highly unpleasant.

The woman was diagnosed with congenital anosmia 鈥� the inability to smell 鈥� when she was 13. Brain imaging revealed she was missing the olfactory bulbs in her forebrain that detect odour information from the nose and transmit it to other parts of the brain involved in smell perception.

Then, when she was 24, she had an unexpected smell awakening. She suddenly began noticing scents like lavender, garlic and manure, with a new smell experience occurring every few weeks. The woman reported feeling disturbed by her new sense, and the fact that she disliked almost all the new smells she encountered increased her anxiety. On one occasion, she felt so overwhelmed she fainted.

A group of smell specialists at the University of Dresden Medical School in Germany conducted tests to try to understand how she had learned to smell.

They presented her with 32 scents and found she could smell half of them. She could detect orange, mint, smoke, turpentine, ginger and lilac, for example, but not coconut, banana, leather, liquorice or cocoa. 鈥淚t鈥檚 not like she only smells food-related things or bad odours, it鈥檚 all over the place,鈥� says 聽at the University of Dresden Medical School, one of her specialists.

Next, they monitored her brain activity when she sniffed rotten egg gas and rose perfume using electroencephalography (EEG). This confirmed that her brain was responding to the odours.

But brain imaging showed she still had no olfactory bulbs, leaving her medical team puzzled.

A 2019 by researchers at the Weizmann Institute of Science in Israel described five women who could smell normally despite having no olfactory bulbs, suggesting the brain can find alternative ways to smell in rare cases. 鈥淏ut the scientific community has been kind of silent on this because no one can explain how,鈥� says Hummel.

The German woman鈥檚 case is even more bizarre since she only developed the ability to smell in adulthood.

Her brain may have created an alternative pathway for smelling that didn鈥檛 require the olfactory bulbs and was somehow suppressed by her hormonal status until she became older, says at the Monell Chemical Senses Center in Philadelphia, who has also been involved in her case.

The reason the woman dislikes her new sense may be because we need to develop positive associations with scents in early life to find them pleasant, says Hummel. For instance, many people like the smell of fir trees because they learned to associate it with Christmas at a young age, he says.

Deaf people also sometimes dislike the first sensation of hearing when they receive cochlear implants because it is so unfamiliar, he says.

The German woman is currently undergoing odour exposure training to help her adjust to her new smelly world. She has already learned to enjoy some aromas like curry by associating them with pleasant experiences like eating.

Her case highlights the plasticity of the brain and hints that other people born without olfactory bulbs may also be able to learn to smell with appropriate training, says Hummel. 鈥淥ur brain is a miraculous thing 鈥� it鈥檚 always full of surprises,鈥� he says.

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