There are some pretty wide variations in how often we wash our hair. While some of us give our locks a good scrub daily, others opt for every other day and many twice-weekly.
But a new TikTok trend suggesting you don't wash your hair for long periods of time is gaining traction with #hairtraining clocking up 169.2m views on the video sharing platform.
It seems there's also a growing focus on styling unwashed locks with hashtags such as #dirtyhair chalking up 264.5m views while #dirtyhairstyle has an incredible 107.1m.
So, is it possible to train your hair to need less washing? "Your scalp is skin and you cannot train any skin to need less washing," advises Anabel Kingsley, trichologist at Philip Kingsley.
"Like the skin on your face, or underarms, it is a living tissue that sweats, produces oils and sheds dead skin cells. Your hair, once grown, is dead tissue."
Which means you can’t actually train it to do anything. But, before we lose you, it’s worth noting that while you cannot train your hair to need less washing you can train yourself to switch up your hair-washing regime. Which could help reduce the build-up of oil that could be hindering your quest for fewer wash days.
What happens to your hair if you wash it less?
"Initially, your hair simply gets dirty, and your scalp greasy,” explains Kingsley. “The long-term implications can be more serious. Your scalp can really suffer health-wise if you are not cleansing it often enough. For instance, you are likely to get itching, flaking, excessive oiliness and general irritation. This can have a knock-on effect on your hair, as scalp health is closely interlinked to hair growth."
What happens to your hair if you wash it more?
Generally speaking, shampooing daily to every other day is ideal.
"It keeps the scalp clean and healthy, and in turn this supports hair growth," advises Kingsley. "Frequent shampooing also removes daily grime and product debris from your hair."
What is the optimum time to leave your hair between washes?
While some content creators on TikTok would have us believe it is 17 days, according to Kingsley we should actually be lathering up daily or every other day minimum.
"That said, if washing your hair more means you are heat-styling more often, you may encounter problems with the condition of your hair," she explains. "It is about finding a balance, but as a general rule, do not leave more than three days between shampoos."
So it isn’t possible to train your hair to need less washing?
Sadly not. "Your scalp is skin and should be given similar care to the skin on your face," explains Kingsley.
Think of hair products as you would make-up, Kingsley suggests.
"You wouldn’t leave foundation or blush sitting on your face for days – and nor should you leave styling mousses or hairsprays on your hair for an extended period."
Watch: 'I only wash my hair with vinegar and my locks are healthier than ever'
How can you help your hair last longer between washes?
Kingsley suggests using a soothing, astringent scalp toner after shampooing to help regulate oil production.
"Once weekly, apply an intensive pre-shampoo conditioning treatment to your hair," she adds. "Alongside your deep conditioner, apply an exfoliating scalp mask to your scalp. Like your face, your scalp benefits from gentle weekly exfoliation," she continues.
Finally, Kingsley recommends only applying conditioner to your mid-lengths and ends. "Applying conditioner to your root area can weigh your hair down and make it limp and flat," she explains.
Is it the case that the more you wash your hair the more you need to wash it?
Not necessarily. "You will simply get used to your hair and scalp looking and feeling a certain way," Kingsley explains. "Again, apply the same logic to hair/scalp as you do to skin. Washing your face frequently does not mean that you will need to wash it more."
So now we’ve got to the bottom of the hair washing dilemma here’s some other barnet busting myths…
Myth: A cold rinse makes hair shinier
Cold rinses may be invigorating, but they do not make your hair shinier. "If anything at all, a cold rinse may be bad for your hair as it constricts the blood capillaries in your scalp which carry nutrients to each follicle," Kingsley explains.
Myth: Hair gets used to the same shampoo
You might think you need to switch up your shampoo brand every so often but in fact a shampoo does not stop working because your hair gets used to it.
"If your shampoo stops giving you the results you want, the condition and needs of your hair have most likely changed," explains Kingsley. "For instance, you may have had it cut, coloured, relaxed, straightened or grown it longer.
"Or the season may have changed, for example, it is more humid, the sun is stronger, or the air is dryer. Your state of health or hormone levels may also be different from recent illness or your monthly cycle."
Myth: Frequent shampooing makes hair oilier
Nope this isn’t true either. "You might as well say that the more you shower, the dirtier you get," Kingsley says.
"Clean hair shows grease faster than hair that is already oily; similarly, clean clothes show dirt immediately, whereas dirty clothes have to get much dirtier before it becomes noticeable. It is a matter of individual perception.
"Just as cleansing an oily face doesn’t produce oiler skin, shampooing does not make your scalp oilier. Things that actually can increase oil production are hormones and stress."
Hair: read more:
The psychology of a haircut as fans praise Susanna Reid’s new style: ‘ageing backwards’ (Yahoo Life UK, 5-min read)
From Helen Mirren's blue hair to Kate's fringe, memorable celebrity hair changes (Yahoo Life UK, 4-min read)
Signs you may have poor scalp health - and what to do about it (Yahoo Life UK, 4-min read)