Overall, people pay little attention to how odor pollution affects health and quality of life. Unpleasant smells are often treated as ordinary and insignificant. Researchers say people value their sense of smell less than sight, hearing, touch, and taste. Some American students even told scientists they would rather lose their sense of smell than their phone.
Recent studies often link unpleasant odors in urban areas with health complaints ranging from headaches and nausea to breathing difficulties and disrupted sleep. Those smells also pose risks of long-term mental and physiological consequences. More scientists are helping explain how bad smells harm our bodies and minds, the BBC reports.
When a Smell Signals Danger
Our sense of smell partly evolved as an early-warning signal that helps us avoid disease and infection. So it’s part of our behavioral immune system, says Johan Lundström, professor of olfactory science at the Karolinska Institute in Sweden.
“The olfactory system primarily functions as an avoidance system, warning us about dangers in the environment,” says Johan Lundström.
In his work, Professor Lundström found that olfactory signals are processed by the brain about 300 milliseconds after a person inhales through the nose.
That protective reaction can make people judge a scent as negative even if they usually find that scent pleasant.
When a scent becomes associated with threat, our sensitivity to it can spike. Professor Lundström noted: “Pairing a scent with an electric shock can make people detect that scent at much lower concentrations.” That reaction probably evolved to help people respond quickly to potential dangers, even when odors are faint.
Health Risks from Bad Smells
Smell isn’t just about detecting threats. Odors have a real impact on people’s health and wellbeing. Scientists have shown that certain odors, such as the scent of a forest, can be beneficial for our mental health. That effect comes from stimulating brain areas linked to emotion and memory.
In 2021, an international team of scientists found some “biological plausibility” for symptoms like headache or vomiting that were caused by unpleasant odors. For example, bad smells can trigger nausea by activating the vagus nerve — the key part of the nervous system that connects the brain and the gut.
How strongly a smell affects our health also depends on how much it bothers us. Pamela Dalton, a cognitive psychologist at the Monell Chemical Senses Center in Philadelphia who has spent 32 years studying smells, says the more you worry about a smell, the more it can affect your health.
How Smells Can Force Lifestyle Changes
Persistent unpleasant odors can push someone to change their lifestyle in ways that harm their health. These changes are known as “maladaptive behaviors.”
For example, a person might feel compelled to keep windows closed on a hot day or avoid going outside or socializing with friends.
However, a smell can be unbearable for some people and barely noticeable to others. Age, gender, allergies, and smoking status are factors closely linked to how people perceive odors.
Regular exposure to unpleasant odors — for example, from landfills — does not make people more tolerant. By contrast, becoming accustomed to neutral or pleasant smells is normal.
“Once you’ve smelled something and realized it won’t kill you, you stop noticing it,” says Professor Lundström.
Why a Good Sense of Smell Matters
A well-functioning sense of smell is an important part of good health. Scientists have long found that a better sense of smell is linked to greater sexual satisfaction. A study from the University of Arkansas found that people with high olfactory sensitivity are more satisfied with their sexual lives.
“Unpleasant smells don’t bother me, because that means my sense of smell is actually working,” says Pamela Dalton.
About 5 percent of people lack a sense of smell (a condition called anosmia, or “olfactory blindness”), and they often face serious health problems. These people are more prone to appetite disorders and are more likely to have poor diets.
What’s more, studies link a poor sense of smell in older adults with a 46 percent higher risk of death within the next 10 years.
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