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.

Mitochondria are tiny structures in cells that convert the food we eat into the energy our cells need to function.

Mitochondrial disease (or mito for short) is a group of conditions that affect this ability to generate the energy organs require to work properly. There are many different forms of mito and depending on the form, it can disrupt one or more organs and can cause organ failure.

There is no cure for mito. But an IVF procedure called mitochondrial donation now offers hope to families affected by some forms of mito that they can have genetically related children free from mito.

After a law to allow mitochondrial donation in Australia was passed in 2022, scientists are now preparing for a clinical trial to see if mitochondrial donation is safe and works.

What is mitochondrial disease?

There are two types of mitochondrial disease.

One is caused by faulty genes in the nuclear DNA, the DNA we inherit from both our parents and which makes us who we are.

The other is caused by faulty genes in the mitochondria’s own DNA. Mito caused by faulty mitochondrial DNA is passed down through the mother. But the risk of disease is unpredictable, so a mother who is only mildly affected can have a child who develops serious disease symptoms.

Mitochondrial disease is the most common inherited metabolic condition affecting one in 5,000 people.

Some people have mild symptoms that progress slowly, while others have severe symptoms that progress rapidly. Mito can affect any organ, but organs that need a lot of energy such as brain, muscle and heart are more often affected than other organs.

Mito that manifests in childhood often involves multiple organs, progresses rapidly, and has poor outcomes. Of all babies born each year in Australia, around 60 will develop life-threatening mitochondrial disease.

What is mitochondrial donation?

Mitochondrial donation is an experimental IVF-based technique that offers people who carry faulty mitochondrial DNA the potential to have genetically related children without passing on the faulty DNA.

It involves removing the nuclear DNA from the egg of someone who carries faulty mitochondrial DNA and inserting it into a healthy egg donated by someone not affected by mito, which has had its nuclear DNA removed.

The resulting egg has the nuclear DNA of the intending parent and functioning mitochondria from the donor. Sperm is then added and this allows the transmission of both intending parents’ nuclear DNA to the child.

A child born after mitochondrial donation will have genetic material from the three parties involved: nuclear DNA from the intending parents and mitochondrial DNA from the egg donor. As a result the child will likely have a reduced risk of mito, or no risk at all.

This highly technical procedure requires specially trained scientists and sophisticated equipment. It also requires both the person with mito and the egg donor to have hormone injections to stimulate the ovaries to produce multiple eggs. The eggs are then retrieved in an ultrasound-guided surgical procedure.

Mitochondrial donation has been pioneered in the United Kingdom where a handful of babies have been born as a result. To date there have been no reports about whether they are free of mito.

Maeve’s Law

After three years of public consultation The Mitochondrial Donation Law Reform (Maeve’s Law) Bill 2021 was passed in the Australian Senate in 2022, making mitochondrial donation legal in a research and clinical trial setting.

Maeve’s law stipulates strict conditions including that clinics need a special licence to perform mitochondrial donation.

To make sure mitochondrial donation works and is safe before it’s introduced into Australian clinical practice, the law also specifies that initial licences will be issued for pre-clinical and clinical trial research and training.

We’re expecting one such licence to be issued for the mitoHOPE (Healthy Outcomes Pilot and Evaluation) program, which we are part of, to perfect the technique and conduct a clinical trial to make sure mitochondrial donation is safe and effective.

Before starting the trial, a preclinical research and training program will ensure embryologists are trained in “real-life” clinical conditions and existing mitochondrial donation techniques are refined and improved. To do this, many human eggs are needed.

The need for donor eggs

One of the challenges with mitochondrial donation is sourcing eggs. For the preclinical research and training program, frozen eggs can be used, but for the clinical trial “fresh” eggs will be needed.

One possible source of frozen eggs is from people who have stored eggs they don’t intend to use.

A recent study looked at data on the outcomes of eggs stored at a Melbourne clinic from 2012 to 2021. Over the ten-year period, 1,132 eggs from 128 patients were discarded. No eggs were donated to research because the clinics where the eggs were stored did not conduct research requiring donor eggs.

However, research shows that among people with stored eggs, the number one choice for what to do with eggs they don’t need is to donate them to research.

This offers hope that, given the opportunity, those who have eggs stored that they don’t intend to use might be willing to donate them to mitochondrial donation preclinical research.

As for the “fresh” eggs needed in the future clinical trial, this will require individuals to volunteer to have their ovaries stimulated and eggs retrieved to give those people impacted by mito a chance to have a healthy baby. Egg donors may be people who are friends or relatives of those who enter the trial, or it might be people who don’t know someone affected by mito but would like to help them conceive.

At this stage, the aim is to begin enrolling participants in the clinical trial in the next 12 to 18 months. However this may change depending on when the required licences and ethics approvals are granted.

Karin Hammarberg, Senior Research Fellow, Global and Women’s Health, School of Public Health & Preventive Medicine, Monash University; Catherine Mills, Professor of Bioethics, Monash University; Mary Herbert, Professor, Anatomy & Developmental Biology, Monash University, and Molly Johnston, Research fellow, Monash Bioethics Centre, Monash University

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