Around one in 20 people has attention-deficit hyperactivity disorder (ADHD). It’s one of the most common neurodevelopmental disorders in childhood and often continues into adulthood.

ADHD is diagnosed when people experience problems with inattention and/or hyperactivity and impulsivity that negatively impacts them at school or work, in social settings and at home.

Some people call the condition attention-deficit disorder, or ADD. So what’s the difference?

In short, what was previously called ADD is now known as ADHD. So how did we get here?

Let’s start with some history

The first clinical description of children with inattention, hyperactivity and impulsivity was in 1902. British paediatrician Professor George Still presented a series of lectures about his observations of 43 children who were defiant, aggressive, undisciplined and extremely emotional or passionate.

Since then, our understanding of the condition evolved and made its way into the Diagnostic and Statistical Manual of Mental Disorders, known as the DSM. Clinicians use the DSM to diagnose mental health and neurodevelopmental conditions.

The first DSM, published in 1952, did not include a specific related child or adolescent category. But the second edition, published in 1968, included a section on behaviour disorders in young people. It referred to ADHD-type characteristics as “hyperkinetic reaction of childhood or adolescence”. This described the excessive, involuntary movement of children with the disorder.

In the early 1980s, the third DSM added a condition it called “attention deficit disorder”, listing two types: attention deficit disorder with hyperactivity (ADDH) and attention deficit disorder as the subtype without the hyperactivity.

However, seven years later, a revised DSM (DSM-III-R) replaced ADD (and its two sub-types) with ADHD and three sub-types we have today:

• predominantly inattentive
• predominantly hyperactive-impulsive
• combined.

Why change ADD to ADHD?

ADHD replaced ADD in the DSM-III-R in 1987 for a number of reasons.

First was the controversy and debate over the presence or absence of hyperactivity: the “H” in ADHD. When ADD was initially named, little research had been done to determine the similarities and differences between the two sub-types.

The next issue was around the term “attention-deficit” and whether these deficits were similar or different across both sub-types. Questions also arose about the extent of these differences: if these sub-types were so different, were they actually different conditions?

Meanwhile, a new focus on inattention (an “attention deficit”) recognised that children with inattentive behaviours may not necessarily be disruptive and challenging but are more likely to be forgetful and daydreamers.

Why do some people use the term ADD?

There was a surge of diagnoses in the 1980s. So it’s understandable that some people still hold onto the term ADD.

Some may identify as having ADD because out of habit, because this is what they were originally diagnosed with or because they don’t have hyperactivity/impulsivity traits.

Others who don’t have ADHD may use the term they came across in the 80s or 90s, not knowing the terminology has changed.

How is ADHD currently diagnosed?

The three sub-types of ADHD, outlined in the DSM-5 are:

• predominantly inattentive. People with the inattentive sub-type have difficulty sustaining concentration, are easily distracted and forgetful, lose things frequently, and are unable to follow detailed instructions
• predominantly hyperactive-impulsive. Those with this sub-type find it hard to be still, need to move constantly in structured situations, frequently interrupt others, talk non-stop and struggle with self control
• combined. Those with the combined sub-type experience the characteristics of those who are inattentive and hyperactive-impulsive.

ADHD diagnoses continue to rise among children and adults. And while ADHD was commonly diagnosed in boys, more recently we have seen growing numbers of girls and women seeking diagnoses.

However, some international experts contest the expanded definition of ADHD, driven by clinical practice in the United States. They argue the challenges of unwanted behaviours and educational outcomes for young people with the condition are uniquely shaped by each country’s cultural, political and local factors.

Regardless of the name change to reflect what we know about the condition, ADHD continues to impact educational, social and life situations of many children, adolescents and adults.

Kathy Gibbs, Program Director for the Bachelor of Education, Griffith University

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

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.