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.

Can you remember a time when you felt stressed leading up to a big life event and then afterwards felt like a weight had been lifted? This process – the ramping up of the stress response and then feeling this settle back down – shows completion of the “stress cycle”.

Some stress in daily life is unavoidable. But remaining stressed is unhealthy. Chronic stress increases chronic health conditions, including heart disease and stroke and diabetes. It can also lead to burnout or depression.

Exercise, cognitive, creative, social and self-soothing activities help us process stress in healthier ways and complete the stress cycle.

What does the stress cycle look like?

Scientists and researchers refer to the “stress response”, often with a focus on the fight-or-flight reactions. The phrase the “stress cycle” has been made popular by self-help experts but it does have a scientific basis.

The stress cycle is our body’s response to a stressful event, whether real or perceived, physical or psychological. It could be being chased by a vicious dog, an upcoming exam or a difficult conversation.

The stress cycle has three stages:

• stage 1 is perceiving the threat
• stage 2 is the fight-or-flight response, driven by our stress hormones: adrenaline and cortisol
• stage 3 is relief, including physiological and psychological relief. This completes the stress cycle.

Different people will respond to stress differently based on their life experiences and genetics.

Unfortunately, many people experience multiple and ongoing stressors out of their control, including the cost-of-living crisis, extreme weather events and domestic violence.

Remaining in stage 2 (the flight-or-flight response), can lead to chronic stress. Chronic stress and high cortisol can increase inflammation, which damages our brain and other organs.

When you are stuck in chronic fight-or-flight mode, you don’t think clearly and are more easily distracted. Activities that provide temporary pleasure, such as eating junk food or drinking alcohol are unhelpful strategies that do not reduce the stress effects on our brain and body. Scrolling through social media is also not an effective way to complete the stress cycle. In fact, this is associated with an increased stress response.

Stress and the brain

In the brain, chronic high cortisol can shrink the hippocampus. This can impair a person’s memory and their capacity to think and concentrate.

Chronic high cortisol also reduces activity in the prefrontal cortex but increases activity in the amygdala.

The prefrontal cortex is responsible for higher-order control of our thoughts, behaviours and emotions, and is goal-directed and rational. The amygdala is involved in reflexive and emotional responses. Higher amygdala activity and lower prefrontal cortex activity explains why we are less rational and more emotional and reactive when we are stressed.

There are five types of activities that can help our brains complete the stress cycle. https://www.youtube.com/embed/eD1wliuHxHI?wmode=transparent&start=0 It can help to understand how the brain encounters stress.

1. Exercise – its own complete stress cycle

When we exercise we get a short-term spike in cortisol, followed by a healthy reduction in cortisol and adrenaline.

Exercise also increases endorphins and serotonin, which improve mood. Endorphins cause an elated feeling often called “runner’s high” and have anti-inflammatory effects.

When you exercise, there is more blood flow to the brain and higher activity in the prefrontal cortex. This is why you can often think more clearly after a walk or run. Exercise can be a helpful way to relieve feelings of stress.

Exercise can also increase the volume of the hippocampus. This is linked to better short-term and long-term memory processing, as well as reduced stress, depression and anxiety.

2. Cognitive activities – reduce negative thinking

Overly negative thinking can trigger or extend the stress response. In our 2019 research, we found the relationship between stress and cortisol was stronger in people with more negative thinking.

Higher amygdala activity and less rational thinking when you are stressed can lead to distorted thinking such as focusing on negatives and rigid “black-and-white” thinking.

Activities to reduce negative thinking and promote a more realistic view can reduce the stress response. In clinical settings this is usually called cognitive behaviour therapy.

At home, this could be journalling or writing down worries. This engages the logical and rational parts of our brain and helps us think more realistically. Finding evidence to challenge negative thoughts (“I’ve prepared well for the exam, so I can do my best”) can help to complete the stress cycle.

3. Getting creative – a pathway out of ‘flight or fight’

Creative activities can be art, craft, gardening, cooking or other activities such as doing a puzzle, juggling, music, theatre, dancing or simply being absorbed in enjoyable work.

Such pursuits increase prefrontal cortex activity and promote flow and focus.

Flow is a state of full engagement in an activity you enjoy. It lowers high-stress levels of noradrenaline, the brain’s adrenaline. When you are focussed like this, the brain only processes information relevant to the task and ignores non-relevant information, including stresses.

4. Getting social and releasing feel-good hormones

Talking with someone else, physical affection with a person or pet and laughing can all increase oxytocin. This is a chemical messenger in the brain that increases social bonding and makes us feel connected and safe.

Laughing is also a social activity that activates parts of the limbic system – the part of the brain involved in emotional and behavioural responses. This increases endorphins and serotonin and improves our mood.

5. Self-soothing

Breathing exercises and meditation stimulate the parasympathetic nervous system (which calms down our stress responses so we can “reset”) via the vagus nerves, and reduce cortisol.

A good cry can help too by releasing stress energy and increasing oxytocin and endorphins.

Emotional tears also remove cortisol and the hormone prolactin from the body. Our prior research showed cortisol and prolactin were associated with depression, anxiety and hostility.

Action beats distraction

Whether it’s watching a funny or sad movie, exercising, journalling, gardening or doing a puzzle, there is science behind why you should complete the stress cycle.

Doing at least one positive activity every day can also reduce our baseline stress level and is beneficial for good mental health and wellbeing.

Importantly, chronic stress and burnout can also indicate the need for change, such as in our workplaces. However, not all stressful circumstances can be easily changed. Remember help is always available.

If you have concerns about your stress or health, please talk to a doctor.

If this article has raised issues for you, or if you’re concerned about someone you know, call Lifeline on 13 11 14 or Kids Helpline on 1800 55 1800.

Theresa Larkin, Associate professor of Medical Sciences, University of Wollongong and Susan J. Thomas, Associate professor in Mental Health and Behavioural Science, University of Wollongong

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