Sun exposure can accelerate ageing, cause skin burns, erythema (a skin reaction), skin cancer, melasmas (or sun spots) and other forms of hyperpigmentation – all triggered by solar ultraviolet radiation.

Approximately 80% of skin cancer cases in people engaged in outdoor activities are preventable by decreasing sun exposure. This can be done in lots of ways including wearing protective clothing or sunscreens.

But not all sunscreens work in the same way. You might have heard of “physical” and “chemical” sunscreens. What’s the difference and which one is right for you?

How sunscreens are classified

Sunscreens are grouped by their use of active inorganic and organic ultraviolet (UV) filters. Chemical sunscreens use organic filters such as cinnamates (chemically related to cinnamon oil) and benzophenones. Physical sunscreens (sometimes called mineral sunscreens) use inorganic filters such as titanium and zinc oxide.

These filters prevent the effects of UV radiation on the skin.

Organic UV filters are known as chemical filters because the molecules in them change to stop UV radiation reaching the skin. Inorganic UV filters are known as physical filters, because they work through physical means, such as blocking, scattering and reflection of UV radiation to prevent skin damage.

Nano versus micro

The effectiveness of the filters in physical sunscreen depends on factors including the size of the particle, how it’s mixed into the cream or lotion, the amount used and the refraction index (the speed light travels through a substance) of each filter.

When the particle size in physical sunscreens is large, it causes the light to be scattered and reflected more. That means physical sunscreens can be more obvious on the skin, which can reduce their cosmetic appeal.

Nanoparticulate forms of physical sunscreens (with tiny particles smaller than 100 nanometers) can improve the cosmetic appearance of creams on the skin and UV protection, because the particles in this size range absorb more radiation than they reflect. These are sometimes labelled as “invisible” zinc or mineral formulations and are considered safe.

So how do chemical sunscreens work?

Chemical UV filters work by absorbing high-energy UV rays. This leads to the filter molecules interacting with sunlight and changing chemically.

When molecules return to their ground (or lower energy) state, they release energy as heat, distributed all over the skin. This may lead to uncomfortable reactions for people with skin sensitivity.

Generally, UV filters are meant to stay on the epidermis (the first skin layer) surface to protect it from UV radiation. When they enter into the dermis (the connective tissue layer) and bloodstream, this can lead to skin sensitivity and increase the risk of toxicity. The safety profile of chemical UV filters may depend on whether their small molecular size allows them to penetrate the skin.

Chemical sunscreens, compared to physical ones, cause more adverse reactions in the skin because of chemical changes in their molecules. In addition, some chemical filters, such as dibenzoylmethane tend to break down after UV exposure. These degraded products can no longer protect the skin against UV and, if they penetrate the skin, can cause cell damage.

Due to their stability – that is, how well they retain product integrity and effectiveness when exposed to sunlight – physical sunscreens may be more suitable for children and people with skin allergies.

Although sunscreen filter ingredients can rarely cause true allergic dermatitis, patients with photodermatoses (where the skin reacts to light) and eczema have higher risk and should take care and seek advice.

What to look for

The best way to check if you’ll have a reaction to a physical or chemical sunscreen is to patch test it on a small area of skin.

And the best sunscreen to choose is one that provides broad-spectrum protection, is water and sweat-resistant, has a high sun protection factor (SPF), is easy to apply and has a low allergy risk.

Health authorities recommend sunscreen to prevent sun damage and cancer. Chemical sunscreens have the potential to penetrate the skin and may cause irritation for some people. Physical sunscreens are considered safe and effective and nanoparticulate formulations can increase their appeal and ease of use.

Yousuf Mohammed, Dermatology researcher, The University of Queensland and Khanh Phan, Postdoctoral research associate, Frazer Institute, The University of Queensland

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

Anorexia nervosa is a severe mental health disorder where people fear weight gain. Those with the disorder have distorted body image and hold rigid beliefs their body is too big. They typically manage this through restricted eating, leading to the serious medical consequences of malnutrition.

Anorexia has one of the highest death rates of any mental illness. Yet there are currently no effective drug treatments and the outcomes of psychotherapy (talk therapy) are poor. So we’re desperately in need of new and improved treatments.

Psilocybin, commonly known as magic mushrooms, is one such novel treatment. But while it shows early promise, you won’t see it used in clinical practice just yet – more research is needed to test if it’s safe and effective.

What does treatment involve?

The treatment involves the patient taking a dose of psilocybin in a safe environment, which is usually a specifically set up clinic. The patient undergoes preparation therapy before the dosing session and integration therapy after.

Psilocybin, extracted from mushrooms, is a psychedelic, which means it can produce altered thinking, sense of time and emotions, and can often result in hallucinations. It also has the potential to shift patients out of their rigid thinking patterns.

Psilocybin is not administered alone but instead with combined structured psychotherapy sessions to help the patient make sense of their experiences and the changes to their thinking. This is an important part of the treatment.

What does the research show?

Research has shown improved effects of psilocybin-assisted psychotherapy after one or two dosing sessions, a couple of weeks apart. Most research to date has targeted depression.

Psilocybin has been found to increase cognitive flexibility – our ability to adjust our thinking patterns according to changing environments or demands. This is one of the ways researchers believe psilocybin might improve symptoms for conditions such as depression and alcohol use disorder, which are marked by rigid thinking styles.

People with anorexia similarly struggle with rigid thinking patterns. So researchers and clinicians have recently turned their attention to anorexia.

In 2023, a small pilot study of ten women with anorexia was published in the journal Nature Medicine. It showed psilocybin-assisted psychotherapy (with 25mg of psilocybin) was safe and acceptable. There were no significant side effects and participants reported having valuable experiences.

Although the trial was not a formal efficacy trial, 40% of the patients did have significant drops in their eating disorder behaviour.

However, the trial only had one dosing session and no long-term follow up, so further research is needed.

A recent animal study using rats examined whether rigid thinking could be improved in rats when given psilocybin. After the psilocybin, rats gained weight and had more flexible thinking (using a reversal learning task).

These positive changes were related to the serotonin neurotransmitter system, which regulates mood, behaviour and satiety (feeling full).

Brain imaging studies in humans show serotonin disturbances in people with anorexia. Psilocybin-assisted psychotherapy is showing promise at modifying the serotonin disturbances and cognitive inflexibility that have been shown to be problematic in anorexia.

Research with animals can provide unique insights into the brain which can sometimes not be investigated in living humans. But animal models can never truly mimic human behaviour and the complex nature of chronic mental health conditions.

What’s next for research?

Further clinical trials in humans are very much needed – and are underway from a research team at the University of Sydney and ours at Swinburne.

Our trial will involve an initial 5mg dose followed by two subsequent doses of 25mg, several weeks apart. An initial low dose aims to help participants prepare for what is likely to be a new and somewhat unpredictable experience.

Our trial will examine the usefulness of providing psychotherapy that directly addresses body image disturbance. We are also investigating if including a family member or close friend in the treatment increases support for their loved one.

Data from other mental health conditions has suggested that not everyone sees benefits, with some people having bad trips and a deterioration in their mental health. So this treatment won’t be for everyone. It’s important to work out who is most likely to respond and under what conditions.

New trials and those underway will be critical in understanding whether psilocybin-assisted psychotherapy is a safe and effective treatment for anorexia, and the optimal conditions to improve the patient’s response. But we are some way off from seeing this treatment in the clinic. One of the big issues being the cost of this intervention and how this will be funded.

Susan Rossell, Director Clinical Trials and Professor Cognitive Neuropsychiatry Centre for Mental Health and Brain Sciences, Swinburne University of Technology and Claire Finkelstein, Clinical Psychologist and PhD candidate, Swinburne University of Technology

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