Why does my sense of smell get much stronger when I'm short of sleep?

April 12, 2023 4:12 PM

I have a poor sense of smell, but it becomes much stronger when I'm short of sleep. There have been many times when I've suddenly been able to smell things I couldn't normally smell and I wondered why I could do that, and then I'd remember I barely slept a wink the night before. It almost seems like the more tired I am, the stronger my sense of smell gets. What could be happening here?
posted by Ursula Hitler to Health & Fitness (14 answers total)

Could you be allergic to something in your room, so the less time you spend in there the less swollen your nasal passages are?
posted by nouvelle-personne at 4:23 PM on April 12, 2023 [1 favorite]

Complete speculation, but maybe your brain is less able to focus and “tune out” certain smells, such that you notice them more intensely?
posted by chocotaco at 5:09 PM on April 12, 2023

Response by poster: I have wondered if it could be my sense of smell somehow compensating for a decrease in acuity in my other senses due to lack of sleep, but that doesn't sound right to me. It's happened in various cities, for as long as I can remember, so I doubt it's related to allergies. It also tends to last throughout the day, FWIW. I'm guessing my normal sense of smell is about 35% of what most people get, so I miss a lot of stuff, but then when I'm short of sleep I'm suddenly smelling things all over the place. I've tried Googling it and I've never found anybody else talking about something like this.
posted by Ursula Hitler at 5:23 PM on April 12, 2023

I'm guessing it's because your cortisol levels are higher, and higher cortisol is associated with better odour perception.
posted by warriorqueen at 5:50 PM on April 12, 2023 [18 favorites]

That's fascinating. I've never heard of this effect, but bodies are all different and react to stimuli in quirky ways.

I find that when I'm sleep-deprived, I feel hungrier, and if I'm not careful, I may start gobbling stuff down almost compulsively. I call it being "slungry", because if I take the time to really examine the sensation I'm feeling, it's kind of a false hunger. It's more like my body seems to be going for food as the best available substitute for what it really needs -- the sleep I'm not giving it.
posted by Artifice_Eternity at 5:51 PM on April 12, 2023 [3 favorites]

My rabbit hole went like this:

- wikipedia page for sense,
- looked at the section called human sensation,
- scrolled to olfactory sense (smell) section,
- Tried a search for the relationship between anosmia and sleep, got nowhere.
- Looked at the search results, decided olfactory nerve was my new keyword.
- Asked the search engine about the relationship between the olfactory nerve and sleep.

This was the first article I found that looked interesting. See if it gives you any clues.

In this review, we describe recent evidence of sleep-dependent changes in olfactory system structure and function which contribute to odor memory and perception.

posted by aniola at 5:52 PM on April 12, 2023 [2 favorites]

What a cool question!

I have nerve damage in my throat which caused the atrocious cough I’ve had for eight years. Certain smells are triggers. With cigarette smoke and bleach among the worst.

Since getting this condition my sense of smell has gotten so sharp that it can be annoying. Like I can be in a room that a smoker was in earlier (but not smoking in) and the stench is overpowering.

I cough because my throat perceives threats , so it makes sense that my smell would become more acute to detect danger. Haven’t asked a Dr but that’s my theory. Perhaps you’re more vulnerable when you haven’t slept and your body gives you more information to keep you safe.
posted by mermaidcafe at 6:43 PM on April 12, 2023 [1 favorite]

When I'm sleep deprived I'm less able to tune out distractions. Things that would ordinarily be background noise are much harder to ignore, smells included.
posted by potrzebie at 8:03 PM on April 12, 2023 [4 favorites]

When sleep deprived I notice greater sensory sensitivity generally, which may rather be difficulty tuning out sensations which normally I don't perceive.
posted by lookoutbelow at 8:43 PM on April 12, 2023 [4 favorites]

A friend of mine with nasal polyps, the kind they used to lasso with wire and pull out (maybe they still do, but this was years ago) told me he could tell they were getting bad when he could hardly smell anything in the morning, but something up in there would let go in the afternoon at some point and he could smell again.

It’s common for nasal passages to swell a bit at night because blood pressure in the nose tends to be higher since the heart is at the same elevation, among other things like exposure to allergens on your pillow,

So maybe when you’re short of sleep your nasal passages open up a little and areas which are usually mostly blocked off come into play.
posted by jamjam at 11:16 PM on April 12, 2023

I don’t have any speculations about the cause, but I also get this. I’ve never really thought about, as I assumed this was just one of the standard very-sleep-deprived things, like getting hot&cold and clammy.
posted by Jon Mitchell at 2:11 AM on April 13, 2023

Just throwing this out there as it seems similar, I tend to get greater sensitivity to smells before I get sick (like a cold). In fact I take it as a sign that I’m about to come down with something when I’m really bothered by cigarette smoke on the street, which I otherwise don’t care about.
posted by vanitas at 7:31 AM on April 13, 2023

Last night when I gave my answer suggesting the possibility of lesser overnight nasal congestion on nights of poor sleep, I had forgotten that human noses contain erectile tissue which responds to putative human pheromones.

And since REM sleep is associated with penile erections, we might expect nasal tissue erections in REM sleep.as well, with consequent congestion and possible blocking of the sense of smell.

And it turns out that REM sleep is associated with greater incidence of obstructive sleep apnea events:

Conclusion: REM sleep is characterized by significant nasal congestion; non-REM sleep, by profound decongestion. This phenomenon may be attributable to REM-dependent variation in cerebral blood flow that affects nasal congestion via the internal carotid system. REM-induced nasal congestion, an indirect effect of augmented cerebral perfusion, may contribute to the higher frequency of obstructive events in REM sleep.

The authors of the linked paper don’t address the issue of nasal tissue erections during REM sleep, but I think it’s reasonable to see them as a possible cause of nasal congestion during that period of sleep whether or not a person is suffering from obstructive sleep apnea.

Sleep is at its shallowest during REM sleep, and I’ve read that people with insomnia are most likely to wake up during that stage, so when you’ve had a night of poor sleep, you probably have more of a deficit of REM sleep than the other stages, and since non-REM sleep is associated with "profound decongestion", after a night in which you "barely slept a wink" you could very well have less nasal congestion than usual, and therefore less blockage of smell receptors than usual.
posted by jamjam at 3:19 PM on April 13, 2023

This happens to me, too!

In my case, it's because of myofascial pain and trigger points. Trigger points are "a hyperirritable spot, a palpable nodule in the taut bands of the skeletal muscles' fascia". You can read a bit more about them here.

The trigger points in my sternocleidomastoid muscle and occipital muscles are very tight and stiff, and lying down exacerbates the tightness. (But you gotta lie down to sleep, unfortunately.) When I sleep fewer hours, the muscles don't get as tight by the time I wake up.

The sternocleidomastoid trigger points (in the front of the neck) can lead to referred sinus pain and nerve compression on the sinus nerves, as well as issues with dizziness, vertigo, and vision. I've found that the occipital trigger points also affect my sinuses: when they're tight, I get congested for no reason, and/or I suddenly can't smell as well as I usually can. Both can lead to referred pain in the head and face.

To sum up, less sleep = less tightness in these trigger points = less compression on the nerves related to my sinuses = miraculously better sense of smell.
posted by fire, water, earth, air at 3:53 AM on April 15, 2023