Would you give up your sense of smell to keep your hair? What about your phone?

A 2022 US study compared smell to other senses (sight and hearing) and personally prized commodities (including money, a pet or hair) to see what people valued more.

The researchers found smell was viewed as much less important than sight and hearing, and valued less than many commodities. For example, half the women surveyed said they’d choose to keep their hair over sense of smell.

Smell often goes under the radar as one of the least valued senses. But it is one of the first sensory systems vertebrates developed and is linked to your mental health, memory and more.

Here are five fascinating facts about your olfactory system.

1. Smell is linked to memory and emotion

Why can the waft of fresh baking trigger joyful childhood memories? And why might a certain perfume jolt you back to a painful breakup?

Smell is directly linked to both your memory and emotions. This connection was first established by American psychologist Donald Laird in 1935 (although French novelist Marcel Proust had already made it famous in his reverie about the scent of madeleines baking.)

Odours are first captured by special olfactory nerve cells inside your nose. These cells extend upwards from the roof of your nose towards the smell-processing centre of your brain, called the olfactory bulb.

From the olfactory bulb they form direct connection with the brain’s limbic system. This includes the amygdala, where emotions are generated, and the hippocampus, where memories are created.

Other senses – such as sight and hearing – aren’t directly connected to the lymbic system.

One 2004 study used functional magnetic resonance imaging to demonstrate odours trigger a much stronger emotional and memory response in the brain than a visual cue.

2. Your sense of smell constantly regenerates

You can lose your ability to smell due to injury or infection – for example during and after a COVID infection. This is known as olfactory dysfunction. In most cases it’s temporary, returning to normal within a few weeks.

This is because every few months your olfactory nerve cells die and are replaced by new cells.

We’re not entirely sure how this occurs, but it likely involves your nose’s stem cells, the olfactory bulb and other cells in the olfactory nerves.

Other areas of your nervous system – including your brain and spinal cord – cannot regenerate and repair after an injury.

Constant regeneration may be a protective mechanism, as the olfactory nerves are vulnerable to damage caused by the external environment, including toxins (such as cigarette smoke), chemicals and pathogens (such as the flu virus).

But following a COVID infection some people might continue to experience a loss of smell. Studies suggest the virus and a long-term immune response damages the cells that allow the olfactory system to regenerate.

3. Smell is linked to mental health

Around 5% of the global population suffer from anosmia – total loss of smell. An estimated 15-20% suffer partial loss, known as hyposmia.

Given smell loss is often a primary and long-term symptom of COVID, these numbers are likely to be higher since the pandemic.

Yet in Australia, the prevalence of olfactory dysfunction remains surprisingly understudied.

Losing your sense of smell is shown to impact your personal and social relationships. For example, it can mean you miss out on shared eating experiences, or cause changes in sexual desire and behaviour.

In older people, declining ability to smell is associated with a higher risk of depression and even death, although we still don’t know why.

4. Loss of smell can help identify neurodegenerative diseases

Partial or full loss of smell is often an early indicator for a range of neurodegenerative diseases, including Alzheimer’s and Parkinson’s diseases.

Patients frequently report losing their sense of smell years before any symptoms show in body or brain function. However many people are not aware they are losing their sense of smell.

There are ways you can determine if you have smell loss and to what extent. You may be able to visit a formal smell testing centre or do a self-test at home, which assesses your ability to identify household items like coffee, wine or soap.

5. You can train your nose back into smelling

“Smell training” is emerging as a promising experimental treatment option for olfactory dysfunction. For people experiencing smell loss after COVID, it’s been show to improve the ability to detect and differentiate odours.

Smell training (or “olfactory training”) was first tested in 2009 in a German psychology study. It involves sniffing robust odours — such as floral, citrus, aromatic or fruity scents — at least twice a day for 10—20 seconds at a time, usually over a 3—6 month period.

Participants are asked to focus on the memory of the smell while sniffing and recall information about the odour and its intensity. This is believed to help reorganise the nerve connections in the brain, although the exact mechanism behind it is unclear.

Some studies recommend using a single set of scents, while others recommend switching to a new set of odours after a certain amount of time. However both methods show significant improvement in smelling.

This training has also been shown to alleviate depressive symptoms and improve cognitive decline both in older adults and those suffering from dementia.

Just like physiotherapy after a physical injury, olfactory training is thought to act like rehabilitation for your sense of smell. It retrains the nerves in your nose and the connections it forms within the brain, allowing you to correctly detect, process and interpret odours.

Lynn Nazareth, Research Scientist in Olfactory Biology, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Drug companies are paying Australian doctors millions of dollars a year to fly to overseas conferences and meetings, give talks to other doctors, and to serve on advisory boards, our research shows.

Our team analysed reports from major drug companies, in the first comprehensive analysis of its kind. We found drug companies paid more than A$33 million to doctors in the three years from late 2019 to late 2022 for these consultancies and expenses.

We know this underestimates how much drug companies pay doctors as it leaves out the most common gift – food and drink – which drug companies in Australia do not declare.

Due to COVID restrictions, the timescale we looked at included periods where doctors were likely to be travelling less and attending fewer in-person medical conferences. So we suspect current levels of drug company funding to be even higher, especially for travel.

What we did and what we found

Since 2019, Medicines Australia, the trade association of the brand-name pharmaceutical industry, has published a centralised database of payments made to individual health professionals. This is the first comprehensive analysis of this database.

We downloaded the data and matched doctors’ names with listings with the Australian Health Practitioner Regulation Agency (Ahpra). We then looked at how many doctors per medical specialty received industry payments and how much companies paid to each specialty.

We found more than two-thirds of rheumatologists received industry payments. Rheumatologists often prescribe expensive new biologic drugs that suppress the immune system. These drugs are responsible for a substantial proportion of drug costs on the Pharmaceutical Benefits Scheme (PBS).

The specialists who received the most funding as a group were cancer doctors (oncology/haematology specialists). They received over $6 million in payments.

This is unsurprising given recently approved, expensive new cancer drugs. Some of these drugs are wonderful treatment advances; others offer minimal improvement in survival or quality of life.

A 2023 study found doctors receiving industry payments were more likely to prescribe cancer treatments of low clinical value.

Our analysis found some doctors with many small payments of a few hundred dollars. There were also instances of large individual payments.

Why does all this matter?

Doctors usually believe drug company promotion does not affect them. But research tells a different story. Industry payments can affect both doctors’ own prescribing decisions and those of their colleagues.

A US study of meals provided to doctors – on average costing less than US$20 – found the more meals a doctor received, the more of the promoted drug they prescribed.

Another study found the more meals a doctor received from manufacturers of opioids (a class of strong painkillers), the more opioids they prescribed. Overprescribing played a key role in the opioid crisis in North America.

Overall, a substantial body of research shows industry funding affects prescribing, including for drugs that are not a first choice because of poor effectiveness, safety or cost-effectiveness.

Then there are doctors who act as “key opinion leaders” for companies. These include paid consultants who give talks to other doctors. An ex-industry employee who recruited doctors for such roles said:

Key opinion leaders were salespeople for us, and we would routinely measure the return on our investment, by tracking prescriptions before and after their presentations […] If that speaker didn’t make the impact the company was looking for, then you wouldn’t invite them back.

We know about payments to US doctors

The best available evidence on the effects of pharmaceutical industry funding on prescribing comes from the US government-run program called Open Payments.

Since 2013, all drug and device companies must report all payments over US$10 in value in any single year. Payment reports are linked to the promoted products, which allows researchers to compare doctors’ payments with their prescribing patterns.

Analysis of this data, which involves hundreds of thousands of doctors, has indisputably shown promotional payments affect prescribing.

US research also shows that doctors who had studied at medical schools that banned students receiving payments and gifts from drug companies were less likely to prescribe newer and more expensive drugs with limited evidence of benefit over existing drugs.

In general, Australian medical faculties have weak or no restrictions on medical students seeing pharmaceutical sales representatives, receiving gifts, or attending industry-sponsored events during their clinical training. They also have no restrictions on academic staff holding consultancies with manufacturers whose products they feature in their teaching.

So a first step to prevent undue pharmaceutical industry influence on prescribing decisions is to shelter medical students from this influence by having stronger conflict-of-interest policies, such as those mentioned above.

A second is better guidance for individual doctors from professional organisations and regulators on the types of funding that is and is not acceptable. We believe no doctor actively involved in patient care should accept payments from a drug company for talks, international travel or consultancies.

Third, if Medicines Australia is serious about transparency, it should require companies to list all payments – including those for food and drink – and to link health professionals’ names to their Ahpra registration numbers. This is similar to the reporting standard pharmaceutical companies follow in the US and would allow a more complete and clearer picture of what’s happening in Australia.

Patients trust doctors to choose the best available treatments to meet their health needs, based on scientific evidence of safety and effectiveness. They don’t expect marketing to influence that choice.

Barbara Mintzes, Professor, School of Pharmacy and Charles Perkins Centre, University of Sydney and Malcolm Forbes, Consultant psychiatrist and PhD candidate, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.