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.

Have you ever been instructed to take your medicine with food and wondered why? Perhaps you’ve wondered if you really need to?

There are varied reasons, and sometimes complex science and chemistry, behind why you may be advised to take a medicine with food.

To complicate matters, some similar medicines need to be taken differently. The antibiotic amoxicillin with clavulanic acid (sold as Amoxil Duo Forte), for example, is recommended to be taken with food, while amoxicillin alone (sold as Amoxil), can be taken with or without food.

Different brands of the same medicine may also have different recommendations when it comes to taking it with food.

Food impacts drug absorption

Food can affect how fast and how much a drug is absorbed into the body in up to 40% of medicines taken orally.

When you have food in your stomach, the makeup of the digestive juices change. This includes things like the fluid volume, thickness, pH (which becomes less acidic with food), surface tension, movement and how much salt is in your bile. These changes can impair or enhance drug absorption.

Eating a meal also delays how fast the contents of the stomach move into the small intestine – this is known as gastric emptying. The small intestine has a large surface area and rich blood supply – and this is the primary site of drug absorption.

Eating a larger meal, or one with lots of fibre, delays gastric emptying more than a smaller meal. Sometimes, health professionals will advise you to take a medicine with food, to help your body absorb the drug more slowly.

But if a drug can be taken with or without food – such as paracetamol – and you want it to work faster, take it on an empty stomach.

Food can make medicines more tolerable

Have you ever taken a medicine on an empty stomach and felt nauseated soon after? Some medicines can cause stomach upsets.

Metformin, for example, is a drug that reduces blood glucose and treats type 2 diabetes and polycystic ovary syndrome. It commonly causes gastrointestinal symptoms, with one in four users affected. To combat these side effects, it is generally recommended to be taken with food.

The same advice is given for corticosteroids (such as prednisolone/prednisone) and certain antibiotics (such as doxycycline).

Taking some medicines with food makes them more tolerable and improves the chance you’ll take it for the duration it’s prescribed.

Can food make medicines safer?

Ibuprofen is one of the most widely used over-the-counter medicines, with around one in five Australians reporting use within a two-week period.

While effective for pain and inflammation, ibuprofen can impact the stomach by inhibiting protective prostaglandins, increasing the risk of bleeding, ulceration and perforation with long-term use.

But there isn’t enough research to show taking ibuprofen with food reduces this risk.

Prolonged use may also affect kidney function, particularly in those with pre-existing conditions or dehydration.

The Australian Medicines Handbook, which guides prescribers about medicine usage and dosage, advises taking ibuprofen (sold as Nurofen and Advil) with a glass of water – or with a meal if it upsets your stomach.

A systematic review published in 2015 found food delays the transit of ibuprofen to the small intestine and absorption, which delays therapeutic effect and the time before pain relief. It also found taking short courses of ibuprofen without food reduced the need for additional doses.

To reduce the risk of ibuprofen causing damage to your stomach or kidneys, use the lowest effective dose for the shortest duration, stay hydrated and avoid taking other non-steroidal anti-inflammatory medicines at the same time.

For people who use ibuprofen for prolonged periods and are at higher risk of gastrointestinal side effects (such as people with a history of ulcers or older adults), your prescriber may start you on a proton pump inhibitor, a medicine that reduces stomach acid and protects the stomach lining.

How much food do you need?

When you need to take a medicine with food, how much is enough?

Sometimes a full glass of milk or a couple of crackers may be enough, for medicines such as prednisone/prednisolone.

However, most head-to-head studies that compare the effects of a medicine “with food” and without, usually use a heavy meal to define “with food”. So, a cracker may not be enough, particularly for those with a sensitive stomach. A more substantial meal that includes a mix of fat, protein and carbohydrates is generally advised.

Your health professional can advise you on which of your medicines need to be taken with food and how they interact with your digestive system.

Mary Bushell, Clinical Associate Professor in Pharmacy, University of Canberra

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