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.

Protecting yourself and family from mosquito bites can be challenging, especially in this hot and humid weather. Protests from young children and fears about topical insect repellents drive some to try alternatives such as wristbands, patches and stickers.

These products are sold online as well as in supermarkets, pharmacies and camping stores. They’re often marketed as providing “natural” protection from mosquitoes.

But unfortunately, they aren’t a reliable way to prevent mosquito bites. Here’s why – and what you can try instead.

Why is preventing mosquito bites important?

Mosquitoes can spread pathogens that make us sick. Japanese encephalitis and Murray Valley encephalitis viruses can have potentially fatal outcomes. While Ross River virus won’t kill you, it can cause potentially debilitating illnesses.

Health authorities recommend preventing mosquito bites by: avoiding areas and times of the day when mosquitoes are most active; covering up with long sleeved shirts, long pants, and covered shoes; and applying a topical insect repellent (a cream, lotion, or spray).

I don’t want to put sticky and smelly repellents on my skin!

While for many people, the “sting” of a biting mosquitoes is enough to prompt a dose of repellent, others are reluctant. Some are deterred by the unpleasant feel or smell of insect repellents. Others believe topical repellents contain chemicals that are dangerous to our health.

However, many studies have shown that, when used as recommended, these products are safe to use. All products marketed as mosquito repellents in Australia must be registered by the Australian Pesticides and Veterinary Medicines Authority; a process that provides recommendations for safe use.

How do topical repellents work?

While there remains some uncertainty about how the chemicals in topical insect repellents actually work, they appear to either block the sensory organs of mosquitoes that drive them to bite, or overpower the smells of our skin that helps mosquitoes find us.

Diethytolumide (DEET) is a widely recommended ingredient in topical repellents. Picaridin and oil of lemon eucalyptus are also used and have been shown to be effective and safe.

How do other products work?

“Physical” insect-repelling products, such as wristbands, coils and candles, often contain a botanically derived chemical and are often marketed as being an alternative to DEET.

However, studies have shown that devices such as candles containing citronella oil provide lower mosquito-bite prevention than topical repellents.

A laboratory study in 2011 found wristbands infused with peppermint oil failed to provide full protection from mosquito bites.

Even as topical repellent formulations applied to the skin, these botanically derived products have lower mosquito bite protection than recommended products such as those containing DEET, picaridin and oil of lemon eucalyptus.

Wristbands infused with DEET have shown mixed results but may provide some bite protection or bite reduction. DEET-based wristbands or patches are not currently available in Australia.

There is also a range of mosquito repellent coils, sticks, and other devices that release insecticides (for example, pyrethroids). These chemicals are primarily designed to kill or “knock down” mosquitoes rather than to simply keep them from biting us.

What about stickers and patches?

Although insect repellent patches and stickers have been available for many years, there has been a sudden surge in their marketing through social media. But there are very few scientific studies testing their efficacy.

Our current understanding of the way insect repellents work would suggest these small stickers and patches offer little protection from mosquito bites.

At best, they may reduce some bites in the way mosquito coils containing botanical products work. However, the passive release of chemicals from the patches and stickers is likely to be substantially lower than those from mosquito coils and other devices actively releasing chemicals.

One study in 2013 found a sticker infused with oil of lemon eucalyptus “did not provide significant protection to volunteers”.

Clothing impregnated with insecticides, such as permethrin, will assist in reducing mosquito bites but topical insect repellents are still recommended for exposed areas of skin.

Take care when using these products

The idea you can apply a sticker or patch to your clothing to protect you from mosquito bites may sound appealing, but these devices provide a false sense of security. There is no evidence they are an equally effective alternative to the topical repellents recommended by health authorities around the world. It only takes one bite from a mosquito to transmit the pathogens that result in serious disease.

It is also worth noting that there are some health warnings and recommendations for their use required by Australian Pesticides and Veterinary Medicines Authority. Some of these products warn against application to the skin (recommending application to clothing only) and to keep products “out of reach of children”. This is a challenge if attached to young children’s clothing.

Similar warnings are associated with most other topical and non-topical mosquito repellents. Always check the labels of these products for safe use recommendations.

Are there any other practical alternatives?

Topical insect repellents are safe and effective. Most can be used on children from 12 months of age and pose no health risks. Make sure you apply the repellent as a thin even coat on all exposed areas of skin.

But you don’t need “tropical strength” repellents for short periods of time outdoors; a range of formulations with lower concentrations of repellent will work well for shorter trips outdoors. There are some repellents that don’t smell as strong (for example, children’s formulations, odourless formulations) or formulations that may be more pleasant to use (for example, pump pack sprays).

Finally, you can always cover up. Loose-fitting long-sleeved shirts, long pants, and covered shoes will provide a physical barrier between you and mosquitoes on the hunt for your or your family’s blood this summer.

Cameron Webb, Clinical Associate Professor and Principal Hospital Scientist, University of Sydney

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