Summer is nearly here. But rather than getting out the sunscreen, some TikTokers are urging followers to chuck it out and go sunscreen-free.

They claim it’s healthier to forgo sunscreen to get the full benefits of sunshine.

Here’s the science really says.

How does sunscreen work?

Because of Australia’s extreme UV environment, most people with pale to olive skin or other risk factors for skin cancer need to protect themselves. Applying sunscreen is a key method of protecting areas not easily covered by clothes.

Sunscreen works by absorbing or scattering UV rays before they can enter your skin and damage DNA or supportive structures such as collagen.

When UV particles hit DNA, the excess energy can damage our DNA. This damage can be repaired, but if the cell divides before the mistake is fixed, it causes a mutation that can lead to skin cancers.

The most common skin cancers are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Melanoma is less common, but is the most likely to spread around the body; this process is called metastasis.

Two in three Australians will have at least one skin cancer in their lifetime, and they make up 80% of all cancers in Australia.

Around 99% of skin cancers in Australia are caused by excessive exposure to UV radiation.

Excessive exposure to UV radiation also affects the appearance of your skin. UVA rays are able to penetrate deep into the skin, where they break down supportive structures such as elastin and collagen.

This causes signs of premature ageing, such as deep wrinkling, brown or white blotches, and broken capillaries.

Sunscreen can help prevent skin cancers

Used consistently, sunscreen reduces your risk of skin cancer and slows skin ageing.

In a Queensland study, participants either used sunscreen daily for almost five years, or continued their usual use.

At the end of five years, the daily-use group had reduced their risk of squamous cell carcinoma by 40% compared to the other group.

Ten years later, the daily use group had reduced their risk of invasive melanoma by 73%

Does sunscreen block the health-promoting properties of sunlight?

The answer is a bit more complicated, and involves personalised risk versus benefit trade-offs.

First, the good news: there are many health benefits of spending time in the sun that don’t rely on exposure to UV radiation and aren’t affected by sunscreen use.

Sunscreen only filters UV rays, not visible light or infrared light (which we feel as heat). And importantly, some of the benefits of sunlight are obtained via the eyes.

Visible light improves mood and regulates circadian rhythm (which influences your sleep-wake cycle), and probably reduces myopia (short-sightedness) in children.

Infrared light is being investigated as a treatment for several skin, neurological, psychiatric and autoimmune disorders.

So what is the benefit of exposing skin to UV radiation?

Exposing the skin to the sun produces vitamin D, which is critical for healthy bones and muscles.

Vitamin D deficiency is surprisingly common among Australians, peaking in Victoria at 49% in winter and being lowest in Queensland at 6% in summer.

Luckily, people who are careful about sun protection can avoid vitamin D deficiency by taking a supplement.

Exposing the skin to UV radiation might have benefits independent of vitamin D production, but these are not proven. It might reduce the risk of autoimmune diseases such as multiple sclerosis or cause release of a chemical that could reduce blood pressure. However, there is not enough detail about these benefits to know whether sunscreen would be a problem.

What does this mean for you?

There are some benefits of exposing the skin to UV radiation that might be blunted by sunscreen. Whether it’s worth foregoing those benefits to avoid skin cancer depends on how susceptible you are to skin cancer.

If you have pale skin or other factors that increase you risk of skin cancer, you should aim to apply sunscreen daily on all days when the UV index is forecast to reach 3.

If you have darker skin that rarely or never burns, you can go without daily sunscreen – although you will still need protection during extended times outdoors.

For now, the balance of evidence suggests it’s better for people who are susceptible to skin cancer to continue with sun protection practices, with vitamin D supplementation if needed.

Katie Lee, PhD Candidate, Dermatology Research Centre, The University of Queensland and Rachel Neale, Principal research fellow, QIMR Berghofer Medical Research Institute

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

The core experiences of depression – changes in energy, activity, thinking and mood – have been described for more than 10,000 years. The word “depression” has been used for about 350 years.

Given this long history, it may surprise you that experts don’t agree about what depression is, how to define it or what causes it.

But many experts do agree that depression is not one thing. It’s a large family of illnesses with different causes and mechanisms. This makes choosing the best treatment for each person challenging.

Reactive vs endogenous depression

One strategy is to search for sub-types of depression and see whether they might do better with different kinds of treatments. One example is contrasting “reactive” depression with “endogenous” depression.

Reactive depression (also thought of as social or psychological depression) is presented as being triggered by exposure to stressful life events. These might be being assaulted or losing a loved one – an understandable reaction to an outside trigger.

Endogenous depression (also thought of as biological or genetic depression) is proposed to be caused by something inside, such as genes or brain chemistry.

Many people working clinically in mental health accept this sub-typing. You might have read about this online.

But we think this approach is way too simple.

While stressful life events and genes may, individually, contribute to causing depression, they also interact to increase the risk of someone developing depression. And evidence shows that there is a genetic component to being exposed to stressors. Some genes affect things such as personality. Some affect how we interact with our environments.

What we did and what we found

Our team set out to look at the role of genes and stressors to see if classifying depression as reactive or endogenous was valid.

In the Australian Genetics of Depression Study, people with depression answered surveys about exposure to stressful life events. We analysed DNA from their saliva samples to calculate their genetic risk for mental disorders.

Our question was simple. Does genetic risk for depression, bipolar disorder, schizophrenia, ADHD, anxiety and neuroticism (a personality trait) influence people’s reported exposure to stressful life events?

You may be wondering why we bothered calculating the genetic risk for mental disorders in people who already have depression. Every person has genetic variants linked to mental disorders. Some people have more, some less. Even people who already have depression might have a low genetic risk for it. These people may have developed their particular depression from some other constellation of causes.

We looked at the genetic risk of conditions other than depression for a couple of reasons. First, genetic variants linked to depression overlap with those linked to other mental disorders. Second, two people with depression may have completely different genetic variants. So we wanted to cast a wide net to look at a wider spectrum of genetic variants linked to mental disorders.

If reactive and endogenous depression sub-types are valid, we’d expect people with a lower genetic component to their depression (the reactive group) would report more stressful life events. And we’d expect those with a higher genetic component (the endogenous group) would report fewer stressful life events.

But after studying more than 14,000 people with depression we found the opposite.

We found people at higher genetic risk for depression, anxiety, ADHD or schizophrenia say they’ve been exposed to more stressors.

Assault with a weapon, sexual assault, accidents, legal and financial troubles, and childhood abuse and neglect, were all more common in people with a higher genetic risk of depression, anxiety, ADHD or schizophrenia.

These associations were not strongly influenced by people’s age, sex or relationships with family. We didn’t look at other factors that may influence these associations, such as socioeconomic status. We also relied on people’s memory of past events, which may not be accurate.

How do genes play a role?

Genetic risk for mental disorders changes people’s sensitivity to the environment.

Imagine two people, one with a high genetic risk for depression, one with a low risk. They both lose their jobs. The genetically vulnerable person experiences the job loss as a threat to their self-worth and social status. There is a sense of shame and despair. They can’t bring themselves to look for another job for fear of losing it too. For the other, the job loss feels less about them and more about the company. These two people internalise the event differently and remember it differently.

Genetic risk for mental disorders also might make it more likely people find themselves in environments where bad things happen. For example, a higher genetic risk for depression might affect self-worth, making people more likely to get into dysfunctional relationships which then go badly.

What does our study mean for depression?

First, it confirms genes and environments are not independent. Genes influence the environments we end up in, and what then happens. Genes also influence how we react to those events.

Second, our study doesn’t support a distinction between reactive and endogenous depression. Genes and environments have a complex interplay. Most cases of depression are a mix of genetics, biology and stressors.

Third, people with depression who appear to have a stronger genetic component to their depression report their lives are punctuated by more serious stressors.

So clinically, people with higher genetic vulnerability might benefit from learning specific techniques to manage their stress. This might help some people reduce their chance of developing depression in the first place. It might also help some people with depression reduce their ongoing exposure to stressors.

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

Jacob Crouse, Research Fellow in Youth Mental Health, Brain and Mind Centre, University of Sydney and Ian Hickie, Co-Director, Health and Policy, Brain and Mind Centre, University of Sydney

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