"Depression hits young girls particularly hard. Here's an explanation I'd never heard."

From the time a girl hits puberty until she’s a middle-aged woman, her likelihood of having an anxiety disorder is twice that of a man. She is also more likely to develop an anxiety disorder earlier in life.

As a child, her chance of suffering anxiety is the same as the boys. But something happens around puberty – just as she becomes a teenager – that heightens her risk.

The same pattern exists for depression. While some of the gender difference in mental health issues can be explained by the tendency of men to not seek help for emotional problems – experts argue that even accounting for this, women experience depression more than men.

A girl is also significantly more prone to develop an eating disorder, particularly anorexia nervosa, than a boy. Anorexia tends to have an early onset, and it can take an average of seven years to recover.  Bulimia and other eating disorders are also far more common in girls.

These mental health issues are highly comorbid – meaning many of them co-occur in the same person. An individual diagnosed with depression is likely to have an anxiety disorder, for example.

Of course, this has devastating impacts for women. It affects their education, their participation, their success at work and their wellbeing.

Listen: Amy Schumer’s confusing marketing messages about body image. Post continues after audio. 

There’s also the corresponding stereotype that young women are erratic, irrational and highly emotional – traits that somewhat trivialise their experiences when they really are suffering. Young girls are perceived as mean and vindictive, superficial and self-obsessed. They’re not taken seriously as a demographic, in spite of their very real and sometimes very dangerous difficulties.

Ever since I learned about these statistics, I’ve been plagued with one question: Why?

Why are girls so vulnerable? What happens to girls as they move from childhood to adulthood, that seems to be so emotionally taxing? What is it about puberty that has such a profound and unique impact on the mental health of females?

Of course, there are several theories. Some believe that the answer is hormonal, but even those who flesh out the hormonal differences between men and women during puberty say that the effect of these differences is somewhat trivial. It’s also not fair to make general assumptions about the impact of hormones – given that hormones differ greatly between individuals and are likely to have unique effects on different individuals.

But there's one explanation I found recently that seems particularly compelling.

The 'cultural ideal hypothesis' suggests that while puberty brings boys closer towards the culturally ideal male body (of being big and strong), puberty moves girls further away from the ideal female body (of being slim).

A normal part of puberty is rapid weight gain, and in the months leading up to their first period, girls grow particularly fast. They're likely to notice more fat on their upper arms, thighs and belly, and they'll develop breasts.

While some people might argue that these changes will give them the ideal 'Kim Kardashian' body, 1) it doesn't - no one looks like Kim Kardashian except Kim Kardashian, and 2) the overwhelming ideal in Western culture looks a little more like this:

???? #tbt

A photo posted by Miranda (@mirandakerr) on Feb 11, 2016 at 4:45pm PST

Which resembles a pre-pubescent girl far more that a post-pubescent one.

Girls, then, inherit a distinct feeling of lacking control. Their growth - something they have very little influence over - is working against them. At the precise moment they start to absorb and value the cultural ideal when it comes to attractiveness, their body starts moving in the opposite direction.

I know this was my experience. My hips broadened and all my clothes were tight. Fat (which was really just skin) hung out over my pants. As my chest grew, I wished it would stop. I wasn't petite anymore. My body hair disgusted me. It was distressing, and as I was coming to terms with my body changing in ways I didn't like, I was bombarded with messages about the importance of attractiveness.

Culturally, girls are ubiquitously taught from a young age that their value relies heavily on their attractiveness. So not only do the unfavourable changes to their body make them feel unattractive, but they fundamentally believe that being attractive is central to their identity. Two researchers named Fredrickson and Roberts even go as far as to say that the cultural ideal of slimness can lead to a chronic state of anxiety in women and girls.

Body dissatisfaction, which in itself might sound quite benign, strongly predicts depression, anxiety, eating disorders, and an array of other emotional problems. We know this. An overwhelming number of studies show this. Yet, for some reason, we think of body dissatisfaction as a normal part of growing up, rather than a dangerous consequence of cultural ideals, that we urgently need to challenge.

For me, this explanation is one I'd personally experienced, but never interrogated. Is the disconnect between how our bodies grow during puberty and how we desperately want to look haunting entire generations of young women?

It's impossible to know for sure.

But it's worth considering how images and messages that seem small can have an overwhelming impact in the long run.