Migraine and our sense of smell — more about an astonishing connection

Do odors trigger migraine attacks? If so, which ones?

For many people in the migraine community, the link between pain and specific odors is nothing new. Some patients report that specific odors trigger migraine attacks. As a result, they try to avoid smells that have had a negative impact in the past. The way people respond to smell is very personal. It is different for everyone. Anything might be a trigger: the smell of a particular flower, kitchen smells, cigarette smoke, car exhaust fumes, a sweet perfume, and more. The scientific term for an aversion to (certain) smells is “osmophobia”, which basically translates as “fear of odor”. Research shows that sensitivity to specific odors is particularly common among people who experience migraines with aura. In contrast, no such connection has been found in people suffering from tension-type headaches.

Smell sensitivity and migraine: a look at the numbers

The relationship between odor sensitivity and migraines was investigated in a Dresden University Hospital study in over 100 participants. The researchers looked at the intensity and frequency of sensitivity to specific smells at different stages of a migraine attack. 62% of participants (nearly two-thirds) reported heightened sensitivity to smells during the pain stage of a migraine episode. 38% experienced this sensitivity even before the pain began. Almost one-third of respondents said they were more sensitive to odors all the time, whether or not they were having a migraine episode.

Approximately half of the patients in the study had migraine with aura. Sensitivity to smell was almost twice as common in this group than in individuals with no aura. Overall, the results of the study suggest that a longer lifetime history of migraine and more severe migraine-related impairment are associated with a greater disease burden and poorer quality of life due to smell sensitivity issues.

The link between smell and pain

Smell sensitivity and pain perception are interlinked at the nervous system level. This also means that these two sensory perceptions affect each other. All the odors a person detects, pleasant or unpleasant, don’t just have an impact on the “smell cells” inside the nose. They may also affect a nerve in your skull called the trigeminal nerve. It provides nerve branches to parts of the face and plays a major role in the pain process. Olfactory (smell-related) cells and the trigeminal nerve are closely linked by nerve pathways. As a result, some stimuli that affect the olfactory system can activate the trigeminal nerve, making a migraine attack more likely.

The close relationship between smell and pain perception is further highlighted by the fact that some people with no sense of smell are also unable to feel pain. This is due to a rare genetic mutation that causes these individuals to lack a specific cell component, called a “sodium channel”. This affects both their sense of smell and their perception of pain.

Can you “unlearn” how to smell?

Does the link between heightened smell sensitivity and migraines mean that migraine patients have a particularly acute sense of smell? Not necessarily. In fact, the opposite appears to be true. A study in this area found that people with migraine consistently had a higher odor detection threshold (“olfactory threshold”) than individuals without migraines. In other words, they only detected smells that were already pretty strong. This was particularly true in patients with aura.

Earlier research showed that, in many migraine sufferers, the olfactory bulb (mentioned above) is slightly smaller than in the general population. Scientists believe this may be because of the odor avoidance strategy of migraine patients, as described earlier. When people with migraine limit their exposure to triggering odors, the brain area responsible for processing these smell signals shrinks over time. You could compare it to a muscle that weakens if it’s not used. In this case, it’s about areas of the brain that are no longer receiving information (smell signals). Without regular input, the involved brain structures become smaller. Interestingly, at the same time, the pain threshold decreases, making these individuals more sensitive to pain.

A possible solution: smell training for migraine sufferers

To explore whether these changes can be influenced, the research team at Dresden University Hospital conducted smell training with migraine patients. Over four weeks, participants were exposed to subjectively pleasant scents multiple times a day. This was done using “sniff sticks” containing fragrances such as rose, vanilla, peach or lavender. Smell perception improved as a result, accompanied by a significant increase in the pain threshold compared to a control group. When exposed to an induced pain stimulus, treated individuals rated the pain as less intense. The authors of the study concluded that smell training might be a potential method for alleviating pain or even preventing migraine attacks. More extensive research is planned to investigate this promising approach in greater depth. We’ll keep you posted!