This is the next article in our ‘Light and health’ series, where we look at how light affects our physical and mental health in sometimes surprising ways. Read other articles in the series.

You’re not feeling well. You’ve had a pounding headache all week, dizzy spells and have vomited up your past few meals.

You visit your GP to get some answers and sit while they shine a light in your eyes, order a blood test and request some medical imaging.

Everything your GP just did relies on light. These are just some of the optical technologies that have had an enormous impact in how we diagnose disease.

1. On-the-spot tests

Point-of-care diagnostics allow doctors to test patients on the spot and get answers in minutes, rather than sending samples to a lab for analysis.

The “flashlight” your GP uses to view the inside of your eye (known as an ophthalmoscope) is a great example. This allows doctors to detect abnormal blood flow in the eye, deformations of the cornea (the outermost clear layer of the eye), or swollen optical discs (a round section at the back of the eye where the nerve link to the brain begins). Swollen discs are a sign of elevated pressure inside your head (or in the worst case, a brain tumour) that could be causing your headaches.

The invention of lasers and LEDs has enabled many other miniaturised technologies to be provided at the bedside or clinic rather than in the lab.

Pulse oximetry is a famous example, where a clip attached to your finger reports how well your blood is oxygenated. It does this by measuring the different responses of oxygenated and de-oxygenated blood to different colours of light.

Pulse oximetry is used at hospitals (and sometimes at home) to monitor your respiratory and heart health. In hospitals, it is also a valuable tool for detecting heart defects in babies.

2. Looking at molecules

Now, back to that blood test. Analysing a small amount of your blood can diagnose many different diseases.

A machine called an automated “full blood count analyser” tests for general markers of your health. This machine directs focused beams of light through blood samples held in small glass tubes. It counts the number of blood cells, determines their specific type, and reports the level of haemoglobin (the protein in red blood cells that distributes oxygen around your body). In minutes, this machine can provide a snapshot of your overall health.

For more specific disease markers, blood serum is separated from the heavier cells by spinning in a rotating instrument called a centrifuge. The serum is then exposed to special chemical stains and enzyme assays that change colour depending on whether specific molecules, which may be the sign of a disease, are present.

These colour changes can’t be detected with the naked eye. However, a light beam from an instrument called a spectrometer can detect tiny amounts of these substances in the blood and determine if the biomarkers for diseases are present, and at what levels.

3. Medical imaging

Let’s re-visit those medical images your GP ordered. The development of fibre-optic technology, made famous for transforming high-speed digital communications (such as the NBN), allows light to get inside the body. The result? High-resolution optical imaging.

A common example is an endoscope, where fibres with a tiny camera on the end are inserted into the body’s natural openings (such as your mouth or anus) to examine your gut or respiratory tracts.

Surgeons can insert the same technology through tiny cuts to view the inside of the body on a video screen during laparoscopic surgery (also known as keyhole surgery) to diagnose and treat disease.

How about the future?

Progress in nanotechnology and a better understanding of the interactions of light with our tissues are leading to new light-based tools to help diagnose disease. These include:

• nanomaterials (materials on an extremely small scale, many thousands of times smaller than the width of a human hair). These are being used in next-generation sensors and new diagnostic tests
• wearable optical biosensors the size of your fingernail can be included in devices such as watches, contact lenses or finger wraps. These devices allow non-invasive measurements of sweat, tears and saliva, in real time
• AI tools to analyse how blood serum scatters infrared light. This has allowed researchers to build a comprehensive database of scatter patterns to detect any cancer
• a type of non-invasive imaging called optical coherence tomography for more detailed imaging of the eye, heart and skin
• fibre optic technology to deliver a tiny microscope into the body on the tip of a needle.

So the next time you’re at the GP and they perform (or order) some tests, chances are that at least one of those tests depend on light to help diagnose disease.

Matthew Griffith, Associate Professor and ARC Future Fellow and Director, UniSA Microscopy and Microanalysis Facilities, University of South Australia

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

We’re all born with mammary glands – better known as breasts. These are made of glandular tissue, fat and the ligaments that attach them to our chest wall.

For roughly half of us – those born biologically female – our breasts will change dramatically in size and shape at puberty. Size is largely genetic: genes explain 56% of the differences in breast size between people. But breasts may also change during pregnancy and breastfeeding, and can be affected by age, diet and exercise.

So, what about bras?

There are a lot of popular beliefs about when, how and what kind of bra to wear to stop your boobs sagging or make them grow. But is there any evidence behind these?

Before we myth bust, let’s get one thing straight: breasts are sisters, not twins. So, while your bra is symmetrical, it’s normal your breasts aren’t.

1. Do bras give you cancer?

No, there is no evidence to show wearing a bra is linked to developing breast cancer.

This myth seems to come from the idea bras can block lymphatic drainage, but there is no evidence to support this or any other cancer-causing mechanism.

One study, involving more than 1,000 women aged 55 to 74, compared those diagnosed with breast cancer to those without. Researchers found no aspect of bra-wearing – including how many hours per day and whether it had an underwire – was linked to breast cancer risk in post-menopausal women.

Risk factors for breast cancer are well established and include being female, over 50 years old, having a family history of breast cancer, and lifestyle factors such as inactivity and drinking a lot of alcohol.

2. Does sleeping in a bra stop your boobs growing?

No. Wearing a bra – day or night – won’t affect their size.

Breasts grow thanks to hormones, which are regulated by your brain. Nutrition and overall health can also play a role; for example, if you lose body fat, your breasts may also shrink.

There is no evidence to suggest sleeping with a bra has a negative effect on their growth.

So, it comes down to comfort. Women with larger breasts may find a bra reduces how much their breasts move during sleep, while others may find it uncomfortable.

3. Will wearing a bra stop my breasts sagging?

No.

Gravity affects everyone, meaning breasts will sag as we age. But larger breasts are affected more by gravitational forces pulling them towards the ground. This may stretch the skin and ligaments over time, making them sag more.

Being pregnant also usually makes your breasts grow bigger and this – along with milk production affecting their composition – can increase strain, potentially stretching skin and ligaments.

Some other factors can also increase this effect, including being older, having a higher body mass index, having multiple pregnancies and smoking. Even surgically reduced breasts sag more with smoking.

However, breastfeeding does not appear to make breasts saggy.

So, while we don’t have evidence to show bras can prevent natural sagging, a well-fitted one may offer support and comfort.

4. Should you only exercise in a sports bra?

Yes. Breasts and bras move with your body. The pull of gravity on your breasts has the potential to cause damage by straining the skin and breaking collagen fibres which support the structure of the breast.

Again, this is more likely to affect women with larger breasts. Researchers found when women with D-cups exercised without a sports bra, their breasts moved up and down about 4 centimetres when walking. When they ran, their breasts bounced about 15cm – the height of your smartphone.

High-impact sports bras are the most effective at reducing breast movement and discomfort, compared to crop tops and everyday bras.

So exercising in a bandeau or “boob tube” bra – like these Roman women in a 4th century mosaic – is not recommended.

5. Can underwire bras injure your boobs?

Yes. It’s possible for underwires from bras to escape their casing and scratch or dig into your breast skin, but this has not been studied.

However, one 2023 study found women who wear underwire bras after breast implants are 2.7 more times likely to have them rupture. This suggests underwire bras can put more pressure on breasts.

One case study in 2014 suggested a tight underwire bra was responsible for blocking and inflaming breast veins, causing pain and breast tissue to harden.

However we don’t have evidence this condition is common, and it can be avoided by wearing correctly fitted bras. If you have breast pain or notice unusual lumps or changes, speak to a doctor.

6. Should I get fitted if I have small breasts?

Yes. Wearing a poorly fitting bra can cause unnecessary discomfort, even if you have small breasts.

One study of 309 Australian women, with bra cup sizes ranging from A to K, found only one in ten were wearing a bra that fitted correctly. This affected women with small, medium, large and extremely large breasts equally.

Most had an incorrectly fitting backband (either too loose or too tight) and the wrong cup size. However women with smaller breasts were more likely to have badly fitting bra straps while women with medium or larger breasts were more likely to have ill-fitting front bands and underwire.

A 2018 review of evidence about women with benign but unidentified breast pain (mastalgia) also found most experienced relief when offered bra-fitting advice and reassurance from their GP.

Amanda Meyer, Senior Lecturer, Anatomy and Pathology in the College of Medicine and Dentistry, James Cook University and Monika Zimanyi, Associate Professor in Anatomy, James Cook University

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