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.

Catherine, Princess of Wales, has announced she has now completed a course of preventive chemotherapy.

The news comes nine months after the princess first revealed she was being treated for an unspecified form of cancer.

In the new video message released by Kensington Palace, Princess Catherine says she’s focused on doing what she can to stay “cancer-free”. She acknowledges her cancer journey is not over and the “path to recovery and healing is long”.

While we don’t know the details of the princess’s cancer or treatment, it raises some questions about how we declare someone fully clear of the disease. So what does being – and staying – “cancer-free” mean?

What’s the difference between being cancer-free and in remission?

Medically, “cancer-free” means two things. First, it means no cancer cells are able to be detected in a patient’s body using the available testing methods. Second, there is no cancer left in the patient.

These might sound basically the same. But this second aspect of “cancer-free” can be complicated, as it’s essentially impossible to be sure no cancer cells have survived a treatment.

It only takes a few surviving cells for the cancer to grow back. But these cells may not be detectable via testing, and can lie dormant for some time. The possibility of some cells still surviving means it is more accurate to say a patient is “in remission”, rather than “cancer-free”.

Remission means there is no detectable cancer left. Once a patient has been in remission for a certain period of time, they are often considered to be fully “cancer-free”.

Princess Catherine was not necessarily speaking in the strict medical sense. Nonetheless, she is clearly signalling a promising step in her recovery.

What happens during remission?

During remission, patients will usually undergo surveillance testing to make sure their cancer hasn’t returned. Detection tests can vary greatly depending on both the patient and their cancer type.

Many tests involve simply looking at different organs to see if there are cancer cells present, but at varying levels of complexity.

Some cancers can be detected with the naked eye, such as skin cancers. In other cases, technology is needed: colonoscopies for colorectal cancers, X-ray mammograms for breast cancers, or CT scans for lung cancers. There are also molecular tests, which test for the presence of cancer cells using protein or DNA from blood or tissue samples.

For most patients, testing will continue for years at regular intervals. Surveillance testing ensures any returning cancer is caught early, giving patients the best chance of successful treatment.

Remaining in remission for five years can be a huge milestone in a patient’s cancer journey. For most types of cancer, the chances of cancer returning drop significantly after five years of remission. After this point, surveillance testing may be performed less frequently, as the patients might be deemed to be at a lower risk of their cancer returning.

Measuring survival rates

Because it is very difficult to tell when a cancer is “cured”, clinicians may instead refer to a “five-year survival rate”. This measures how likely a cancer patient is to be alive five years after their diagnosis.

For example, data shows the five-year survival rate for bowel cancer among Australian women (of all ages) is around 70%. That means if you had 100 patients with bowel cancer, after five years you would expect 70 to still be alive and 30 to have succumbed to the disease.

These statistics can’t tell us much about individual cases. But comparing five-year survival rates between large groups of patients after different cancer treatments can help clinicians make the often complex decisions about how best to treat their patients.

The likelihood of cancer coming back, or recurring, is influenced by many factors which can vary over time. For instance, approximately 30% of people with lung cancer develop a recurrent disease, even after treatment. On the other hand, breast cancer recurrence within two years of the initial diagnosis is approximately 15%. Within five years it drops to 10%. After ten, it falls below 2%.

These are generalisations though – recurrence rates can vary greatly depending on things such as what kind of cancer the patient has, how advanced it is, and whether it has spread.

Staying cancer-free

Princess Catherine says her focus now is to “stay cancer-free”. What might this involve?

How a cancer develops and whether it recurs can be influenced by things we can’t control, such as age, ethnicity, gender, genetics and hormones.

However, there are sometimes environmental factors we can control. That includes things like exposure to UV radiation from the sun, or inhaling carcinogens like tobacco.

Lifestyle factors also play a role. Poor diet and nutrition, a lack of exercise and excessive alcohol consumption can all contribute to cancer development.

Research estimates more than half of all cancers could potentially be prevented through regular screening and maintaining a healthy lifestyle (not to mention preventing other chronic conditions such as heart disease and diabetes).

Recommendations to reduce cancer risk are the same for everyone, not just those who’ve had treatment like Princess Catherine. They include not smoking, eating a nutritious and balanced diet, exercising regularly, cutting down on alcohol and staying sun smart.

Amali Cooray, PhD Candidate in Genetic Engineering and Cancer, WEHI (Walter and Eliza Hall Institute of Medical Research) ; John (Eddie) La Marca, Senior Research Officer, Blood Cells and Blood Cancer, WEHI (Walter and Eliza Hall Institute of Medical Research) , and Sarah Diepstraten, Senior Research Officer, Blood Cells and Blood Cancer Division, WEHI (Walter and Eliza Hall Institute of Medical Research)

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