Head hair comes in many colours, shapes and sizes, and hairstyles are often an expression of personal style or cultural identity.

Many different genes determine our hair texture, thickness and colour. But some people’s hair changes around the time of puberty, pregnancy or after chemotherapy.

So, what can cause hair to become curlier, thicker, thinner or grey?

Curly or straight? How hair follicle shape plays a role

Hair is made of keratin, a strong and insoluble protein. Each hair strand grows from its own hair follicle that extends deep into the skin.

Curly hair forms due to asymmetry of both the hair follicle and the keratin in the hair.

Follicles that produce curly hair are asymmetrical and curved and lie at an angle to the surface of the skin. This kinks the hair as it first grows.

The asymmetry of the hair follicle also causes the keratin to bunch up on one side of the hair strand. This pulls parts of the hair strand closer together into a curl, which maintains the curl as the hair continues to grow.

Follicles that are symmetrical, round and perpendicular to the skin surface produce straight hair.

Life changes, hair changes

Our hair undergoes repeated cycles throughout life, with different stages of growth and loss.

Each hair follicle contains stem cells, which multiply and grow into a hair strand.

Head hairs spend most of their time in the growth phase, which can last for several years. This is why head hair can grow so long.

Let’s look at the life of a single hair strand. After the growth phase is a transitional phase of about two weeks, where the hair strand stops growing. This is followed by a resting phase where the hair remains in the follicle for a few months before it naturally falls out.

The hair follicle remains in the skin and the stems cells grow a new hair to repeat the cycle.

Each hair on the scalp is replaced every three to five years.

Hormone changes during and after pregnancy alter the usual hair cycle

Many women notice their hair is thicker during pregnancy.

During pregnancy, high levels of oestrogen, progesterone and prolactin prolong the resting phase of the hair cycle. This means the hair stays in the hair follicle for longer, with less hair loss.

A drop in hormones a few months after delivery causes increased hair loss. This is due to all the hairs that remained in the resting phase during pregnancy falling out in a fairly synchronised way.

Hair can change around puberty, pregnancy or after chemotherapy

This is related to the genetics of hair shape, which is an example of incomplete dominance.

Incomplete dominance is when there is a middle version of a trait. For hair, we have curly hair and straight hair genes. But when someone has one curly hair gene and one straight hair gene, they can have wavy hair.

Hormonal changes that occur around puberty and pregnancy can affect the function of genes. This can cause the curly hair gene of someone with wavy hair to become more active. This can change their hair from wavy to curly.

Researchers have identified that activating specific genes can change hair in pigs from straight to curly.

Chemotherapy has very visible effects on hair. Chemotherapy kills rapidly dividing cells, including hair follicles, which causes hair loss. Chemotherapy can also have genetic effects that influence hair follicle shape. This can cause hair to regrow with a different shape for the first few cycles of hair regrowth.

Hormonal changes as we age also affect our hair

Throughout life, thyroid hormones are essential for production of keratin. Low levels of thyroid hormones can cause dry and brittle hair.

Oestrogen and androgens also regulate hair growth and loss, particularly as we age.

Balding in males is due to higher levels of androgens. In particular, high dihydrotestosterone (sometimes shortened to DHT), which is produced in the body from testosterone, has a role in male pattern baldness.

Some women experience female pattern hair loss. This is caused by a combination of genetic factors plus lower levels of oestrogen and higher androgens after menopause. The hair follicles become smaller and smaller until they no longer produce hairs.

Reduced function of the cells that produce melanin (the pigment that gives our hair colour) is what causes greying.

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.

TikTok is full of videos that demonstrate DIY hacks, from up-cycling tricks to cooking tips. Meanwhile, a growing number of TikTok videos offer tips to help you save money and time at the dentist. But do they deliver?

Here are five popular dental TikTok trends and why you might treat them with caution.

1. Home-made whitening solutions

Many TikTok videos provide tips to whiten teeth. These include tutorials on making your own whitening toothpaste using ingredients such as hydrogen peroxide, a common household bleaching agent, and baking soda (sodium bicarbonate).

In this video, the influencer says:

And then you’re going to pour in your hydrogen peroxide. There’s really no measurement to this.

But hydrogen peroxide in high doses is poisonous if swallowed, and can burn your gums, mouth and throat, and corrode your teeth.

High doses of hydrogen peroxide may infiltrate holes or microscopic cracks in your teeth to inflame or damage the nerves and blood vessels in the teeth, which can cause pain and even nerve death. This is why dental practitioners are bound by rules when we offer whitening treatments.

Sodium bicarbonate and hydrogen peroxide are among the components in commercially available whitening toothpastes. While these commercial products may be effective at removing surface stains, their compositions are carefully curated to keep your smile safe.

2. Oil pulling

Oil pulling involves swishing one tablespoon of sesame or coconut oil in your mouth for up to 20 minutes at a time. It has roots in Ayurvedic medicine, a traditional medicine practice that originates from the Indian subcontinent.

While oil pulling should be followed by brushing and flossing, I’ve had patients who believe oil pulling is a replacement for these practices.

There has been some research on the potential of oil pulling to treat gum disease or other diseases in the mouth. But overall, evidence that supports the effectiveness of oil pulling is of low certainty.

For example, studies that test the effectiveness of oil pulling have been conducted on school-aged children and people with no dental problems, and often measure dental plaque growth over a few days to a couple of weeks.

Chlorhexidine is an ingredient found in some commercially available mouthwashes.
In one study, people who rinsed with chlorhexidine mouthwash (30 seconds twice daily) developed less plaque on their teeth compared to those who undertook oil pulling for eight to 10 minutes.

Ultimately, it’s unlikely you will experience measurable gain to your oral health by adding oil pulling to your daily routine. If you’re time-poor, you’re better off focusing on brushing your teeth and gums well alongside flossing.

3. Using rubber bands to fix gaps

This TikTok influencer shows his followers he closed the gaps between his front teeth in a week using cheap clear rubber bands.

But this person may be one of the lucky few to successfully use bands to close a gap in his teeth without any mishaps. Front teeth are slippery and taper near the gums into cone-shaped roots. This can cause bands to slide and disappear into the gums to surround the tooth roots, which can cause infections and pain.

If this happens, you may require surgery that involves cutting your gums to remove the bands. If the bands have caused an infection, you may lose the affected teeth. So it’s best to leave this sort of work to a dental professional trained in orthodontics.

4. Filing or cutting teeth to shape them

My teeth hurt just watching this video.

Cutting or filing teeth unnecessarily can expose the second, more sensitive tooth layer, called dentine, or potentially, the nerve and blood vessels inside the tooth. People undergoing this sort of procedure could experience anything from sensitive teeth through to a severe toothache that requires root canal treatment or tooth removal.

You may notice dentist drills spray water when cutting to protect your teeth from extreme heat damage. The drill in this video is dry with no water used to cool the heat produced during cutting.

It may also not be sterile. We like to have everything clean and sterile to prevent contaminated instruments used on one patient from potentially spreading an infection to another person.

Importantly, once you cut or file your teeth away, it’s gone forever. Unlike bone, hair or nails, our teeth don’t have the capacity to regrow.

5. DIY fillings

Many people on TikTok demonstrate filling cavities (holes) or replacing gaps between teeth with a material made from heated moulded plastic beads. DIY fillings can cause a lot of issues – I’ve seen this in my clinic first hand.

While we may make it look simple in dental surgeries, the science behind filling materials and how we make them stick to teeth to fill cavities is sophisticated.

Filling a cavity with the kind of material made from these beads will be as effective as using sticky tape on sand. Not to mention the cavity will continue to grow bigger underneath the untreated “filled” teeth.

I know it’s easy to say “see a dentist about that cavity” or “go to an orthodontist to fix that gap in your teeth you don’t like”, but it can be expensive to actually do these things. However if you end up requiring treatment to fix the issues caused at home, it may end up costing you much more.

So what’s the take-home message? Stick with the funny cat and dog videos on TikTok – they’re safer for your smile.

Arosha Weerakoon, Senior Lecturer and General Dentist, School of Dentistry, The University of Queensland

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