Strong smells and migraine

Trigger and osmophobia

These are two different claims:

• A smell as a trigger. You smell something, then an attack starts.
• Osmophobia. During an attack, odours that are not unpleasant at other times become unpleasant (Zanchin 2005).

There is a third case in between. The Migraine Trust lists being more sensitive to smell among prodrome symptoms. In that phase the attack has begun but the pain has not, and an ordinary smell may seem like the cause.

What studies show

Study	Design	People	Result
Kelman 2007	Retrospective clinic data	1,207 with migraine	43.7% named perfume or odour as a trigger, 35.7% smoke
Silva-Néto 2012	Cross-sectional convenience sample, thesis abstract	200 with migraine, 200 with tension-type headache	Odour-triggered headache in 70.0% with migraine, none with tension-type headache. Pain began a mean of 25.5 minutes after exposure
Zanchin 2007	Clinic series	807 with migraine, 198 with tension-type headache	Osmophobia during attacks in 43.0% with migraine, none with tension-type headache
Terrin 2020	Prospective, 4 attacks per person	193 people, 772 attacks	Osmophobia in 45.7% of migraine-without-aura attacks, none of 124 tension-type attacks

Percentages vary with method. Terrin notes that published figures for osmophobia run up to 95%. The Silva-Néto abstract reports osmophobia in 86.0% with migraine and 6.0% with tension-type headache, so not every sample shows zero. Only 46% of people enrolled in that study completed it, and the Silva-Néto figure comes from a thesis abstract with a non-random sample, so treat it as a rough indication.

Which smells. Among 140 people with odour-triggered headache, perfume was named by 75.7%, paint by 42.1%, gasoline by 28.6% and bleach by 27.1% (Silva-Néto 2012). In osmophobia, people named scents (63.9%), food, most often coffee (55.2%), and cigarette smoke (54.8%) (Zanchin 2007).

Osmophobia also has diagnostic interest. Terrin reports that ICHD-2 proposed it as an accompanying symptom of migraine and that ICHD-3 no longer mentions it, and recommends including it in the diagnostic criteria because of its specificity.

Why a trigger is hard to prove

• Early sensitivity. At a Hamburg clinic, people with smell sensitivity before the headache named odours as a trigger significantly more often than others (p under 0.0001). The authors suggest that such triggers may be misread symptoms. The data were retrospective (Schulte 2015).
• Mimicry. A 2018 review lists sensitivity to odours among premonitory symptoms that may mimic triggers (Marmura 2018).
• No controlled data here. The sources for this page contain no blinded study in which a smell was given and attacks were counted. Surveys record what people believe caused an attack.
• Overlap with symptoms. The Migraine Trust says it can be hard to tell whether odours are a trigger or a symptom, because people become more sensitive to them during an attack.

These sources do not establish a mechanism.

How to check it in your diary

1. Name the smell and the place, for example perfume on a train or paint at home.
2. Write the order. Was this smell stronger or more unpleasant than usual for you? That may be early sensitivity, not a cause.
3. Time the gap from exposure to first symptom. Fix your window in advance, so that you do not widen it to fit.
4. Log the setting. A stuffy room, a long trip or a missed meal may coincide with the smell.
5. Count exposures with no attack. Every ordinary day near perfume counts.

If smells seem to limit your daily life, take the record to your doctor. For the general method, see how to test a suspected trigger.