Timothy C. Hain, MD, Chicago IL. • Page last modified: December 3, 2022
See also: sensory sensitivity in migraine •
Osmophobia means "abnormal sensitivity to smell". Perhaps more precisely, it is fear of smell. While sound sensitivity is divided up into a variety of subcategories -- for example, misophonia, hyperacusis, phonophobia, this doesn't seem to have been paid as much attention to with smell.
Osmophobia is an uncommon symptom with few causes.
There are many other senses and smell sensitivity is just one of many possibilities.
|Sound||Hyperacusis||Phonophobia||LDL||Correlates with smell sensitivity (Rocho-Filho et al, 2016)|
|Smell||Smell sensitivity||Osmophobia||Upsit, Sniffit|
|Weather||Barosensitivity||? Barophobia ?|
|Motion sensitivity||kinesiophobia||Motion sickness||Various questionnaires||Motion sickness can trigger smell sensitivity|
Here we are going to mainly concentrate on migraine, but we will try to put it into context with other smell disorders.
Smell sensitivity is rare, and usually attributed to migraine or psychological conditions. However, sometimes it is reported in motion sickness, and presumably there is come cross-over with other sensory sensitivities that accompany other medical conditions (e.g. pregnancy, liver failure). Smell sensitivity also occurs in "multiple chemical sensitivity" (Alobid et al, 2014) According to Henkin et al, patients with Cystic fibrosis have lowered thresholds to taste and smell (1962).
Increased sensitivity to smell as well as other irritants may be a personality characteristic -- Bell et al (1994) suggested that "cacosmia" -- sensitivity to environmental chemical odors was associated with high ratings for stress in the first 4 decades of life, as well as increased prevalence of physician-diagnosed nasal allergies, breast cysts, hypothyroidism, sinusitis, food sensitivities, irritable bowel, and migraine headache. We suspect there is something to the idea that there are individuals who have a sensitive personality style.
Smell sensitivity ordinarily goes down with age. (Seow et al, 2016).
The technology of measurement of measuring sensory hypersensitivity is probably best worked out for sound, where assessment of "LDL" or loudness discomfort levels are routine when fitting hearing aids.
One would think that for all of these situations, one should "adjust" the discomfort level for the threshold -- or in other words, attempt to differentiate between the input to the brain and the response to the brain. For hearing, this can be done by subtracting the pure tone threshold from the LDL. This simple concept does not seem to have penetrated into the literature about other senses.
As is the case with sound and light sensitivity, for measurement, there is an attempt to distinguish between having a lower threshold, and having greater discomfort. There are also instruments that identify substances that one can detect. This is called "discrimination". The UPSIT smell identification test is one way to assess -- this is a "scratch and sniff" technology type test. It costs about $30/patient to administer, so perhaps not the most appropriate method for a clinic. Another test that may be more cost effective is the "sniffin sticks". These are multiple use.
For smell in particular, thresholds vary with nasal congestion and age. Older people can't smell as well as younger people, and persons with clogged noses can't smell much of anything. Neurodegenerative disorders such as Alzheimer's disease or Parkinson's disease, may start with loss of sense of smell, many years before there is measurable cognitive decline. Interestingly, AD patients don't know that they can't smell, showing that subjective instruments cannot be relied upon. (Nordin et al, 1995)
Another consideration is that as is the case with light, sound, and other senses, during a migraine, smell may be more bothersome to migraine patients.
Demarquay et al (2006) used the term "hedonicity" for the pleasentness of smells, and reported that patients with olfactory hypersensitivity judged odors less pleasant, but of equal intencity. Saisu et al (2011) reported how "offensive" odors were to migraine patients, and noted that perfume, rose and Japanese cypress odors were more "offensive to migraine patients" than controls. One would naturally wonder if patients with migraine might be conditioned to dislike strong odors, because of the association with pain. In other words, perhaps this is a learned response.
Similarly to loud noise, motion, or strong light, strong smells have been reported to cause migraines.
Blau and Solomon (1985) reported that odors, pleasant or otherwise, could precipitate migraine in 11 out of 50 patients. Kelman reported that perfume or odor triggers migraine in about 50%.
The general consensus is that smell is very specific but insensitive. Here we are talking about the offensiveness of odors, not whether or not they can be detected.
Finally, some patients with migraine, as is the case as with light, may have an "olfactory aura". (Diamond et al, 1985; Coleman et al, 2011; Mainardi et al, 2016).
Figure 2 from Snyder and Drummond (1997).
Snyder and Drummond (1997) compared 20 patients with migraine, mainly women, with 21 patients with fewer than 8 headaches per year. They found that patients with migraine or migraine with aura had slightly lower thresholds to vanillin than controls. The migraine patients did not find acetone more unpleasant than controls.
Hirsch (1992) reported that 18% of patients were low or unable to smell Pyridine. This is somewhat opposite to Synder and Drummond, but perhaps there is something special about Pyridine. Somewhat similarly, Marmura et al (2014) reported that about 25% of their 42 migraine attack subjects reported a drop in their sense of smell during attacks. Again, Whiting et al (2015) reported that migraine subjects were slieghtly less sensitive to the UPSIT test on both migraine and non-migraine days. Contrary to these observations, Harriott (2014) suggested that Migraineurs report sensitivity to odors during and between attacks (this is a vague statement), and also quoted the same paper as above (Snyder and Drummond) to suggest that acetone "is detected at lower concentrations in migraineurs who report osmosensitivity". Perhaps there are two groups of migraine patients - -those with smell sensitivity and those without ? This would fit into the general conjecture that "migraine" is not a single disorder. If we adopt this idea however, we need to do a lot more "splitting".
It would seem from these data that smell intensity ratings are unlikely to be useful for migraine diagnosis, but might be useful to separate out a subgroup.
Little is written about this. A general discussion of treatment of sensory sensitivity is found here.
Approaches unique to smell sensitivity include "chemical cauterization" to remove the nasal mucosa (every 3 months). While zinc nasal spray is known to reduce smell sensitivity (Chang and Patel, 2022) , this is not recommended or even commercially available as it is reported to (sometimes) result in loss of smell entirely. The "Zicam" nasal spray, marketed for the common cold, was taken off the market in 2009 because the FDA warned of loss of smell. This was based on a small study in an alternative health journal (Eby et al, 2006). We are unaware of any studies concerning purposeful use of zinc nasal spray to decreased olfaction. We think it is likely that treatment of hypersensitivity to smell has just been neglected, although zinc nasal spray would seem to be logical.