And razors should never be tapped on a sink under any circumstances

Tests have shown people should start by shaving in direction of the hair

The Gillette scientist has also revealed the do's and don'ts of shaving

Her footage reveals what happens as multi-blade razors move over hairs

Dr Kristina Vanoosthuyze studies the shaving habits of 80 men every day using high-speed cameras at Gillette's Innovation Centre in Reading

When it comes to shaving, boys are normally taught the art by their fathers or older brothers.

But this means bad habits can also be passed down through generations.

Now a principal scientist from Gillette has revealed the science behind shaving including how hairs behave, why washing the skin is so vital and why you should never, ever tap your razor on the sink.

She also settles the debate about whether you should go with, or against the grain.

Scroll down for video

Beard hairs are, on average, a tenth of a millimetre in diameter. When dry, the hair is around 130 microns in diameter (left) but when hydrated this expands to almost 150 microns. Washing the face before a shave increases the surface area the blades can cut through said Gillette principal scientist Kristina Vanoosthuyze

Dr Kristina Vanoosthuyze has worked in the Gillette Shaving Technology area at the Innovation Centre in Reading for the past nine years.

Every morning 80 volunteers visit the centre and shave in front of a filming rig that combines magnifying lenses, high-speed cameras and special high-intensity lighting.

This has revealed how the blade cuts through the hair, and in the case of multiple-blade models, the first blade pulls the hair up, the second cuts it, the third blade acts in a similar way to the first, and so on.

In some of their products, Gillette also offers a vibrate function that further lifts the hair and reduces the friction caused by the blades.

This footage has also revealed the differences between dry and hydrated skin and beard hair.

Every day 80 volunteers shave in front of a rig that combines magnifying lenses and high-speed cameras. This has revealed how the blade cuts through the hair. In the case of multiple-blade models, the first blade pulls the hair up, the second cuts it, the third blade pulls and so on

When hydrated, skin is also tighter (an image of the skin is shown before washing left and after washing right). This exposes more of the hair's surface area to the blade. As a result Dr Kristina Vanoosthuyze recommends showering before shaving - and not the other way round

This image is a microscopic image of cut hairs on dehydrated skin. Dry hair can have the strength of copper wire and when hair and skin hydrates it swells and makes the hair easier to cut. Additionally, the lubricating ingredients in a shaving gel reduce friction between blade and skin, improving glide

Beard hairs are, on average, a tenth of a millimetre in diameter. When dry, the hair is around 130 microns but when hydrated this expands to almost 150 microns.

This increases the surface area that the blades can cut through, and when hydrated, skin is plumper, which reveals more of the hair.

HOW TO GET THE PERFECT SHAVE Before the shave, hydrate the hair by washing the skin with a gentle cleanser: This softens the hair and significantly reduces the force needed to cut it. Apply plenty of shave gel: This provides a protective anti-friction layer and improves razor glide for a smoother, more comfortable shave. Shave with a multi-blade razor using light strokes: Gillette said the razor should do the work, not the person shaving. Change direction: Begin by shaving with the grain of the hair before switching and going against this grain. Make sure blades are not old or dull: The lifespan of razors can vary depending on how often they are used and how hard. As a general rule if the razor begins to drag or doesn't cut as closely as before, replace the blades. Use aftershave: This can be any product containing moisturiser to rehydrate and comfort the skin. Many aftershaves contain alcohol that acts as an astringent to sterilise the skin and provide a barrier against infection. Advertisement

As a result it makes more sense to shower before shaving and not the other way round.

'Allowing water to penetrate the hair is key for a comfortable and close shave because dry hair is difficult to cut,' explained Dr Vanoosthuyze.

'In fact, dry hair can have the strength of copper wire. When hair hydrates, it swells and becomes easier to cut.

'So, men should wash the face and neck with a mild cleanser before the shave. Or at least take a shower before the shave and not the other way around.

'Additionally, the lubricating ingredients formulated in a shaving gel reduce friction between blade and skin, improving razor glide for a more comfortable shaving experience.'

Scanning electron microscopy also highlights how hairs and follicles differ on the cheek, neck and chin, for example.

On the cheek these hairs resemble the shape of an egg, while on the chin they are wider on the underside than the top.

The hairs of the neck look similar to those on the chin but are thicker and more robust.

The skin on the cheek is also flatter than the raised bumps on the neck.

This suggest that shaving in one direction on the cheek may not have the same affect when used on the neck, for example.

However, Dr Vanoosthuyze revealed that shaving in the direction of the hair is often the best place to start.

'It is difficult to give a simple, straightforward answer, because the comfort of the shave - or lack of irritation - is dependent on so many more factors than simply the direction of the shaving stroke,' she told MailOnline at the launch of Gillette's Fusion ProGlide with FlexBall technology razor.

'Our data has shown that men who shave with ProGlide against the grain rated the product as high for 'gives a comfortable shave' as those men who shaved with the grain and/or in both directions.'

Scanning electron microscopy also highlights how hairs and follicles differ on the cheek, neck and chin (pictured). On the cheek these hairs resemble the shape of an egg, while on the chin they are wider on the underside than the top. The hairs of the neck look similar to those on the chin but are thicker and more robust

The skin on the cheek is also flatter than the raised bumps on the neck (pictured). Dr Vanoosthuyze said: 'As a general rule, most men find shaving first in the direction of the hair growth and then following up with upstrokes provides the closest, smoothest shave with good skin comfort'

But she continued that a man's facial hair tends to grow in different directions, so even if he thinks he shaves with the grain, some hairs will still unknowingly be cut against the grain.

'As a general rule, I would say that most men find using light strokes and shaving first in the direction of the hair growth and then following up with upstrokes provides the closest, smoothest shave with good skin comfort.'

And when it comes on what not to do, Dr Vanoosthuyze said that some men place as much as 3.3lbs (1.5kg) of force on the blade.

'The closeness of the shave is largely determined by the quality and design of the razor, not by how hard you press,' she added.

'The best way for a close, comfortable shave is to use gentle strokes. The razor should do the work, not you.'

Dr Vanoosthuyze also explained that under no circumstances should a person tap their razor on the side of the sink. Tapping the razor causes the precision blades to misalign which affects the cutting quality, but also how long the blades will last. This image shows the angle a blade takes on a typical cheek hair

She also explained that under no circumstances should you tap the razor on the side of the sink.

Tapping the razor causes the precision blades to misalign which affects the cutting quality, but also how long the blades will last.

'At the end of the shave, just rinse the razor thoroughly with water and shake off excess water before storing,' Dr Vanoosthuyze.

And after the shave, Dr Vanoosthuyze recommends using a moisturising lotion.

'A good moisturiser will leave the skin soft and smooth and help to maintain the skin's natural moisture barrier.'