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.

People often believe they are allergic to house dust. But of the 20% of Australians suffereing with allergies, a number are are actually allergic to microscopic house dust mites.

House dust mites belong to the same family as spiders and ticks. They measure just 0.2-0.3 mm, with 50 fitting on a single pinhead. They live for 65–100 days, and females lay 60–100 eggs in their life.

House dust mites love temperate climates and humidity. They feed off the skin cells we and animals shed, as well as mould, which they digest using special enzymes. These enzymes are excreted in their poo about 20 times a day. They also shed fragments of their exoskeletons.

All these fragments trigger allergies in people with this type of allergic rhinitis (which is also known as hay fever)

What are the symptoms?

When people with house dust mite allergy inhale the allergens, they penetrate the mucous membranes of the airways and eyes. Their body recognises the allergens as a threat, releasing chemicals including one called histamine.

This causes symptoms including a runny nose, an itchy nose, eyes and throat, sneezing, coughing and a feeling of mucus at the back of your throat (known as a post-nasal drip).

People with this type of allergy usually mouth breath, snore, rub their nose constantly (creating a nasal crease called the “dust mite salute”) and have dark shadows under their eyes.

House dust mite allergy can also cause poor sleep, constant tiredness, reduced concentration at work or school and lower quality of life.

For people with eczema, their damaged skin barrier can allow house dust mite proteins in. This prompts immune cells in the skin to release chemicals which make already flared skin become redder, sorer and itchier, especially in children.

Symptoms of house dust mite allergy occur year round, and are often worse after going to bed and when waking in the morning. But people with house dust mite allergy and pollen allergies find their year-round symptoms worsen in spring.

How is it diagnosed?

House dust mite allergy symptoms often build up over months, or even years before people seek help. But an accurate diagnosis means you can not only access the right treatment – it’s also vital for minimising exposure.

Doctor and nurse practitioners can order a blood test to check for house dust mite allergy.

Alternatively, health care providers with specialised allergy training can perform skin prick tests. This involves placing drops of the allergens on the arm, along with a positive and negative “control”. After 15 minutes, those who test positive will have developed a mosquito bite-like mark.

How is it treated?

Medication options include one or a combination of:

• daily non-sedating antihistamines
• a steroid nasal spray
• allergy eye drops.

Your health care professional will work with you to develop a rhinitis (hay fever) medical management plan to reduce your symptoms. If you’re using a nasal spray, your health provider will show you how to use it, as people often use it incorrectly.

If you also have asthma or eczema which is worsened by dust mites, your health provider will adapt your asthma action plan or eczema care plan accordingly.

If you experience severe symptoms, a longer-term option is immunotherapy. This aims to gradually turn off your immune system’s ability to recognise house dust mites as a harmful allergen.

Immunotherapy involves taking either a daily sublingual tablet, under the tongue, or a series of injections. Injections require monthly attendances over three years, after the initial weekly build-up phase.

These are effective, but are costly (as well as time-consuming). So it’s important to weigh up the potential benefits and downsides with your health-care provider.

How can you minimise house dust mites?

There are also important allergy minimisation measures you can take to reduce allergens in your home.

Each week, wash your bedding and pyjamas in hot water (over 60°C). This removes house dust mite eggs and debris.

Opt for doonas, covers or quilts that can be washed in hot water above 60°C. Alternatively, low-cost waterproof or leak proof covers can keep house dust mites out.

If you can, favour blinds and wood floors over curtains and carpet. Dust blinds and surfaces with a damp cloth each week and vacuum while wearing a mask, or have someone else do it, as house dust mites can become airborne during cleaning.

But beware of costly products with big marketing budgets and little evidence to support their use. A new mattress, for example, will always be house dust mite-free. But once slept on, the house dust mite life cycle can start.

Mattress protectors and toppers commonly claim to be “hypoallergenic”, “anti-allergy” or “allergy free”. But their pore sizes are not small enough to keep house dust mites and their poo out, or shed skin going through.

Sprays claiming to kill mites require so much spray to penetrate the product that it’s likely to become wet, may smell like the spray and, unless dried properly, may grow mould.

Finally, claims that expensive vacuum cleaners can extract all the house dust mites are unsubstantiated.

For more information, visit healthdirect.gov.au or the Australian Society of Clinical Immunology and Allergy.

Deryn Lee Thompson, Eczema and Allergy Nurse; Lecturer, University of South Australia

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