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.

Few topics are more debated in health than the value of the humble bathroom scale. Some experts advocate daily self-weigh-ins to promote accountability for weight management, particularly when we’re following a diet and exercise program to lose weight.

Others suggest ditching self-weigh-ins altogether, arguing they can trigger negative psychological responses and unhealthy behaviours when we don’t like, or understand, the number we see on the scale.

Many, like me, recommend using scales to weigh yourself weekly, even when we’re not trying to lose weight. Here’s why.

1. Weighing weekly helps you manage your weight

Research confirms regular self-weighing is an effective weight loss and management strategy, primarily because it helps increase awareness of our current weight and any changes.

A systematic review of 12 studies found participants who weighed themselves weekly or daily over several months lost 1–3 BMI (body mass index) units more and regained less weight than participants who didn’t weight themselves frequently. The weight-loss benefit was evident with weekly weighing; there was no added benefit with daily weighing.

Self-weigh-ins are an essential tool for weight management as we age. Adults tend to gain weight progressively through middle age. While the average weight gain is typically between 0.5–1kg per year, this modest accumulation of weight can lead to obesity over time. Weekly weighing and keeping track of the results helps avoid unnecessary weight gain.

Tracking our weight can also help identify medical issues early. Dramatic changes in weight can be an early sign of some conditions, including problems with our thyroid, digestion and diabetes.

2. Weekly weighing accounts for normal fluctuations

Our body weight can fluctuate within a single day and across the days of the week. Studies show body weight fluctuates by 0.35% within the week and it’s typically higher after the weekend.

Daily and day-to-day body weight fluctuations have several causes, many linked to our body’s water content. The more common causes include:

The type of food we’ve consumed

When we’ve eaten a dinner higher in carbohydrates, we’ll weigh more the next day. This change is a result of our bodies temporarily carrying more water. We retain 3–4 grams of water per gram of carbohydrate consumed to store the energy we take from carbs.

Our water content also increases when we consume foods higher in salt. Our bodies try to maintain a balance of sodium and water. When the concentration of salt in our bloodstream increases, a mechanism is triggered to restore balance by retaining water to dilute the excess salt.

Our food intake

Whether it’s 30 grams of nuts or 65 grams of lean meat, everything we eat and drink has weight, which increases our body weight temporarily while we digest and metabolise what we’ve consumed.

Our weight also tends to be lower first thing in the morning after our food intake has been restricted overnight and higher in the evening after our daily intake of food and drinks.

Exercise

If we weigh ourselves at the gym after a workout, there’s a good chance we’ll weigh less due to sweat-induced fluid loss. The amount of water lost varies depending on things like our workout intensity and duration, the temperature and humidity, along with our sweat rate and hydration level. On average, we lose 1 litre of sweat during an hour of moderate-intensity exercise.

Hormonal changes

Fluctuations in hormones within your menstrual cycle can also affect fluid balance. Women may experience fluid retention and temporarily gain 0.5–2kg of weight at this time. Specifically, the luteal phase, which represents the second half of a woman’s cycle, results in a shift of fluid from your blood plasma to your cells, and bloating.

Bowel movements

Going to the bathroom can lead to small but immediate weight loss as waste is eliminated from the body. While the amount lost will vary, we generally eliminate around 100 grams of weight through our daily bowel movements.

All of these fluctuations are normal, and they’re not indicative of significant changes in our body fat or muscle mass. However, seeing these fluctuations can lead to unnecessary stress and a fixation with our weight.

3. Weekly weighing avoids scale obsession and weight-loss sabotage

Weighing too frequently can create an obsession with the number on the scales and do more harm than good.

Often, our reaction when we see this number not moving in the direction we want or expect is to further restrict our food intake or embark on fad dieting. Along with not being enjoyable or sustainable, fad diets also ultimately increase our weight gain rather than reversing it.

This was confirmed in a long-term study comparing intentional weight loss among more than 4,000 twins. The researchers found the likelihood of becoming overweight by the age of 25 was significantly greater for a twin who dieted to lose 5kg or more. This suggests frequent dieting makes us more susceptible to weight gain and prone to future weight gain.

So what should you do?

Weighing ourselves weekly gives a more accurate measure of our weight trends over time.

Aim to weigh yourself on the same day, at the same time and in the same environment each week – for example, first thing every Friday morning when you’re getting ready to take a shower, after you’ve gone to the bathroom, but before you’ve drunk or eaten anything.

Use the best quality scales you can afford. Change the batteries regularly and check their accuracy by using a “known” weight – for example, a 10kg weight plate. Place the “known” weight on the scale and check the measurement aligns with the “known” weight.

Remember, the number on the scale is just one part of health and weight management. Focusing solely on it can overshadow other indicators, such as how your clothes fit. It’s also essential to pay equal attention to how we’re feeling, physically and emotionally.

Stop weighing yourself – at any time interval – if it’s triggering anxiety or stress, and get in touch with a health-care professional to discuss this.

At the Boden Group, Charles Perkins Centre, we are studying the science of obesity and running clinical trials for weight loss. You can register here to express your interest.

Nick Fuller, Charles Perkins Centre Research Program Leader, University of Sydney

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