What do chocolate chip cookies smell like to you? To me, there are few smells more heavenly than a pan of fresh chocolately goodness right out of the oven. It's a smell of rich, sweet decadence that makes my taste buds tingle. It smells like happiness.
Most other smells really bother me. The pungent bouquet of cut flowers, sizzling bacon, air fresheners, perfume, cleaning products, even fresh-mowed grass all drive my nose batty. Many of them trigger migraines if I'm around them long enough. A neurologist once told me I was a "super smeller." She likely meant I have a heightened sensitivity to smell known as hyperosmia. People with hyperosmia have an extreme sense of smell to the point that many smells cause discomfort while some people are debilitated by odors.
My weird nose makes me wonder if cookies smell the same to everyone else. Just like is my blue really your blue, is my chocolate chip cookie smell really the same as your chocolate chip cookie smell? Or do you just smell what I smell when there's chicken in the oven?
Smell perception in the genes
A new study by researchers from the Monell Chemical Senses Center found that the different ways we experience smells is in our DNA. Published in the Proceedings of the National Academy of Sciences, the study found that small changes in just one olfactory receptor gene can affect how strong or pleasant an odor is for one person.
Every person's nose has about 400 different types of specialized sensor proteins, known as olfactory receptors. One smell can activate several different of these receptors, and receptors can be activated by several different smells. The brain interprets these receptor activation patterns to identify millions (maybe trillions) of different smells.
"We still know very little about how olfactory receptors translate information from an odor molecule into the perception of an odor's quality, intensity, and pleasantness,' said senior author Joel Mainland, Ph.D., an olfactory neurobiologist at Monell, in a news release. "By examining how variation in an olfactory receptor gene changes odor perception, we can begin to understand the function of each receptor. This in turn will help us learn how the receptors work together so that we can decipher the olfactory code and digitize olfaction."
For the study, researchers asked 332 people to rate how they perceived the intensity and pleasantness of nearly 70 odors. Researchers also collected DNA samples from all the participants. They used genetic information to identify people who had broken forms of certain receptors and compared their odor reception to people who had normal versions of the same receptor. They wanted to find out if the same odor appeared more pleasant or not as strong or both.
Scientists were surprised to find that a change in a single gene could inspire differences in how people perceived the same smell.
"Because most odors activate several receptors, many scientists thought that losing one receptor wouldn't make a difference in how we perceive that odor. Instead, our work shows that is not the case and changes to a single receptor can make a big difference in how you perceive an odor," said Mainland.
What about phantom smells?
Interestingly, not only are there people who smell things differently than other people, there are also people who smell odors that aren't there at all. These olfactory hallucinations are called phantosmia.
Some phantosmia are pleasant and some are foul, reports the Mayo Clinic. Sometimes the smells can come and go; some people have them constantly.
They can happen after an upper respiratory infection or a head injury. Phantosmia also can be caused by temporal lobe seizures, inflamed sinuses, brain tumors and Parkinson's disease. Some patients report an "aura," which is like a premonition that the smells are going to happen, according to an article in JAMA Otolaryngology.
Often, people report that the first time it happens, it only lasts for a few minutes. It will usually recur for longer periods and more frequently after that.
When someone experiences phantosmia, nothing they do can typically make the smell go away. Everything they eat even has that flavor.
Some people try to treat the olfactory hallucinations with sleep, nasal drops, antidepressant or anti-anxiety medication or even surgery. The treatments are rarely successful, but the condition is considered harmless.
There's a similar smell disorder called parosmia. This is where you perceive a smell as something totally different than it should smell. For example, something that normally smells pleasant to you now smells foul or something familiar smells like something else. Chocolate chip cookies now smell like burnt toast.
That's when life just isn't fair.