Summer is nearly here. But rather than getting out the sunscreen, some TikTokers are urging followers to chuck it out and go sunscreen-free.

They claim it’s healthier to forgo sunscreen to get the full benefits of sunshine.

Here’s the science really says.

How does sunscreen work?

Because of Australia’s extreme UV environment, most people with pale to olive skin or other risk factors for skin cancer need to protect themselves. Applying sunscreen is a key method of protecting areas not easily covered by clothes.

Sunscreen works by absorbing or scattering UV rays before they can enter your skin and damage DNA or supportive structures such as collagen.

When UV particles hit DNA, the excess energy can damage our DNA. This damage can be repaired, but if the cell divides before the mistake is fixed, it causes a mutation that can lead to skin cancers.

The most common skin cancers are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Melanoma is less common, but is the most likely to spread around the body; this process is called metastasis.

Two in three Australians will have at least one skin cancer in their lifetime, and they make up 80% of all cancers in Australia.

Around 99% of skin cancers in Australia are caused by excessive exposure to UV radiation.

Excessive exposure to UV radiation also affects the appearance of your skin. UVA rays are able to penetrate deep into the skin, where they break down supportive structures such as elastin and collagen.

This causes signs of premature ageing, such as deep wrinkling, brown or white blotches, and broken capillaries.

Sunscreen can help prevent skin cancers

Used consistently, sunscreen reduces your risk of skin cancer and slows skin ageing.

In a Queensland study, participants either used sunscreen daily for almost five years, or continued their usual use.

At the end of five years, the daily-use group had reduced their risk of squamous cell carcinoma by 40% compared to the other group.

Ten years later, the daily use group had reduced their risk of invasive melanoma by 73%

Does sunscreen block the health-promoting properties of sunlight?

The answer is a bit more complicated, and involves personalised risk versus benefit trade-offs.

First, the good news: there are many health benefits of spending time in the sun that don’t rely on exposure to UV radiation and aren’t affected by sunscreen use.

Sunscreen only filters UV rays, not visible light or infrared light (which we feel as heat). And importantly, some of the benefits of sunlight are obtained via the eyes.

Visible light improves mood and regulates circadian rhythm (which influences your sleep-wake cycle), and probably reduces myopia (short-sightedness) in children.

Infrared light is being investigated as a treatment for several skin, neurological, psychiatric and autoimmune disorders.

So what is the benefit of exposing skin to UV radiation?

Exposing the skin to the sun produces vitamin D, which is critical for healthy bones and muscles.

Vitamin D deficiency is surprisingly common among Australians, peaking in Victoria at 49% in winter and being lowest in Queensland at 6% in summer.

Luckily, people who are careful about sun protection can avoid vitamin D deficiency by taking a supplement.

Exposing the skin to UV radiation might have benefits independent of vitamin D production, but these are not proven. It might reduce the risk of autoimmune diseases such as multiple sclerosis or cause release of a chemical that could reduce blood pressure. However, there is not enough detail about these benefits to know whether sunscreen would be a problem.

What does this mean for you?

There are some benefits of exposing the skin to UV radiation that might be blunted by sunscreen. Whether it’s worth foregoing those benefits to avoid skin cancer depends on how susceptible you are to skin cancer.

If you have pale skin or other factors that increase you risk of skin cancer, you should aim to apply sunscreen daily on all days when the UV index is forecast to reach 3.

If you have darker skin that rarely or never burns, you can go without daily sunscreen – although you will still need protection during extended times outdoors.

For now, the balance of evidence suggests it’s better for people who are susceptible to skin cancer to continue with sun protection practices, with vitamin D supplementation if needed.

Katie Lee, PhD Candidate, Dermatology Research Centre, The University of Queensland and Rachel Neale, Principal research fellow, QIMR Berghofer Medical Research Institute

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

When we start to go grey depends a lot on genetics.

Your first grey hairs usually appear anywhere between your twenties and fifties. For men, grey hairs normally start at the temples and sideburns. Women tend to start greying on the hairline, especially at the front.

The most rapid greying usually happens between ages 50 and 60. But does anything we do speed up the process? And is there anything we can do to slow it down?

You’ve probably heard that plucking, dyeing and stress can make your hair go grey – and that redheads don’t. Here’s what the science says.

What gives hair its colour?

Each strand of hair is produced by a hair follicle, a tunnel-like opening in your skin. Follicles contain two different kinds of stem cells:

• keratinocytes, which produce keratin, the protein that makes and regenerates hair strands
• melanocytes, which produce melanin, the pigment that colours your hair and skin.

There are two main types of melanin that determine hair colour. Eumelanin is a black-brown pigment and pheomelanin is a red-yellow pigment.

The amount of the different pigments determines hair colour. Black and brown hair has mostly eumelanin, red hair has the most pheomelanin, and blonde hair has just a small amount of both.

So what makes our hair turn grey?

As we age, it’s normal for cells to become less active. In the hair follicle, this means stem cells produce less melanin – turning our hair grey – and less keratin, causing hair thinning and loss.

As less melanin is produced, there is less pigment to give the hair its colour. Grey hair has very little melanin, while white hair has none left.

Unpigmented hair looks grey, white or silver because light reflects off the keratin, which is pale yellow.

Grey hair is thicker, coarser and stiffer than hair with pigment. This is because the shape of the hair follicle becomes irregular as the stem cells change with age.

Interestingly, grey hair also grows faster than pigmented hair, but it uses more energy in the process.

Can stress turn our hair grey?

Yes, stress can cause your hair to turn grey. This happens when oxidative stress damages hair follicles and stem cells and stops them producing melanin.

Oxidative stress is an imbalance of too many damaging free radical chemicals and not enough protective antioxidant chemicals in the body. It can be caused by psychological or emotional stress as well as autoimmune diseases.

Environmental factors such as exposure to UV and pollution, as well as smoking and some drugs, can also play a role.

Melanocytes are more susceptible to damage than keratinocytes because of the complex steps in melanin production. This explains why ageing and stress usually cause hair greying before hair loss.

Scientists have been able to link less pigmented sections of a hair strand to stressful events in a person’s life. In younger people, whose stems cells still produced melanin, colour returned to the hair after the stressful event passed.

4 popular ideas about grey hair – and what science says

1. Does plucking a grey hair make more grow back in its place?

No. When you pluck a hair, you might notice a small bulb at the end that was attached to your scalp. This is the root. It grows from the hair follicle.

Plucking a hair pulls the root out of the follicle. But the follicle itself is the opening in your skin and can’t be plucked out. Each hair follicle can only grow a single hair.

It’s possible frequent plucking could make your hair grey earlier, if the cells that produce melanin are damaged or exhausted from too much regrowth.

2. Can my hair can turn grey overnight?

Legend says Marie Antoinette’s hair went completely white the night before the French queen faced the guillotine – but this is a myth.

Melanin in hair strands is chemically stable, meaning it can’t transform instantly.

Acute psychological stress does rapidly deplete melanocyte stem cells in mice. But the effect doesn’t show up immediately. Instead, grey hair becomes visible as the strand grows – at a rate of about 1 cm per month.

Not all hair is in the growing phase at any one time, meaning it can’t all go grey at the same time.

3. Will dyeing make my hair go grey faster?

This depends on the dye.

Temporary and semi-permanent dyes should not cause early greying because they just coat the hair strand without changing its structure. But permanent products cause a chemical reaction with the hair, using an oxidising agent such as hydrogen peroxide.

Accumulation of hydrogen peroxide and other hair dye chemicals in the hair follicle can damage melanocytes and keratinocytes, which can cause greying and hair loss.

4. Is it true redheads don’t go grey?

People with red hair also lose melanin as they age, but differently to those with black or brown hair.

This is because the red-yellow and black-brown pigments are chemically different.

Producing the brown-black pigment eumelanin is more complex and takes more energy, making it more susceptible to damage.

Producing the red-yellow pigment (pheomelanin) causes less oxidative stress, and is more simple. This means it is easier for stem cells to continue to produce pheomelanin, even as they reduce their activity with ageing.

With ageing, red hair tends to fade into strawberry blonde and silvery-white. Grey colour is due to less eumelanin activity, so is more common in those with black and brown hair.

Your genetics determine when you’ll start going grey. But you may be able to avoid premature greying by staying healthy, reducing stress and avoiding smoking, too much alcohol and UV exposure.

Eating a healthy diet may also help because vitamin B12, copper, iron, calcium and zinc all influence melanin production and hair pigmentation.

Theresa Larkin, Associate Professor of Medical Sciences, University of Wollongong

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