The latest on nanoparticles in sunscreens.

The UV filters TiO2 and ZnO have been used in sunscreens for decades, and are particularly valuable because they give broad-spectrum protection from sunlight. In an attempt to make sunscreens more cosmetically acceptable, the particle sizes of these metal oxides are often reduced to NPs measuring 1-100 millionth of a millimetre. Both TiO2 and ZnO NP can generate reactive oxygen species after sun exposure, which can cause cell damage and cell death if produced in excess or not neutralised. This can be minimised to some extent by coating the NPs in aluminium hydroxide, polymers and inert oxides of silica, or adding anti-oxidants such as Vitamin A, C, E. In Australia, all active ingredients must be declared on sunscreen labels, however, it is not a requirement to declare the particle size of the active ingredients. The outcomes of the Literature Review on the safety of titanium dioxide and zinc oxide NPs in sunscreens is available on the TGA website. They concluded that on current evidence, neither TiO2 nor ZnO NPs are likely to cause harm when used in sunscreens. The current state of knowledge strongly dictates that the minor risks potentially associated with NPs in sunscreen are vastly outweighed by the benefits they afford against sun damage and skin cancer. The Australian Government Department of Health and the Therapeutic Goods Administration (TGA) recently released a review based on the latest scientific literature regarding the safety of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) in sunscreens. The main issues considered were evidence for the ability of these NPs to penetrate the skin and their potential toxicity. They stated that the majority of in vitro studies (using animal and human skin) show that both TiO2 and ZnO NPs either do not penetrate or minimally penetrate the layers of the skin, suggesting that systemic absorption and toxicity is highly unlikely.

The latest on nanoparticles in sunscreens.

The UV filters TiO2 and ZnO have been used in sunscreens for decades, and are particularly valuable because they give broad-spectrum protection from sunlight. In an attempt to make sunscreens more cosmetically acceptable, the particle sizes of these metal oxides are often reduced to NPs measuring 1-100 millionth of a millimetre. Both TiO2 and ZnO NP can generate reactive oxygen species after sun exposure, which can cause cell damage and cell death if produced in excess or not neutralised. This can be minimised to some extent by coating the NPs in aluminium hydroxide, polymers and inert oxides of silica, or adding anti-oxidants such as Vitamin A, C, E.

In Australia, all active ingredients must be declared on sunscreen labels, however, it is not a requirement to declare the particle size of the active ingredients. The outcomes of the Literature Review on the safety of titanium dioxide and zinc oxide NPs in sunscreens is available on the TGA website. They concluded that on current evidence, neither TiO2 nor ZnO NPs are likely to cause harm when used in sunscreens. The current state of knowledge strongly dictates that the minor risks potentially associated with NPs in sunscreen are vastly outweighed by the benefits they afford against sun damage and skin cancer.

The Australian Government Department of Health and the Therapeutic Goods Administration (TGA) recently released a review based on the latest scientific literature regarding the safety of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) in sunscreens. The main issues considered were evidence for the ability of these NPs to penetrate the skin and their potential toxicity. They stated that the majority of in vitro studies (using animal and human skin) show that both TiO2 and ZnO NPs either do not penetrate or minimally penetrate the layers of the skin, suggesting that systemic absorption and toxicity is highly unlikely.

Sun worshippers beware: tanning may be addictive!

The researchers shaved the backs of the mice and gave them a daily dose of UV light (enough to induce tanning but not burning) for six weeks. The study found that bloodstream endorphin levels rose within a week, and regular exposure to UV radiation led to physical dependence and addictive behaviour in the mice. The animals even exhibited withdrawal symptoms (shaking, tremors and teeth chattering) after being treated with a drug that blocked the endorphin activity.

Although the study involved laboratory mice, the researchers said they believe the findings were applicable to humans because the biological response of human skin to UV radiation is similar. In theory, sun-related skin cancer should be highly preventable merely by reducing exposure, but the addictive qualities of UV exposure may help explain the “sun-seeking behaviour” some people display through outdoor and indoor tanning and other pursuits despite the known risks.

Fell GL, Robinson KC et al. Skin β-endorphin mediates addiction to UV light. Cell 2014; 157:1527-34.

How to choose and use sunscreens.

Here are our top 10 tips for understanding, choosing and using sunscreens:

  1. What does SPF mean? The SPF (sun protection factor) is a measure of how much ultraviolet B (UVB) protection the sunscreen offers. UVB is the main wavelength in sunlight that causes sunburn. SPF is calculated by taking the time it takes you to burn with a sunscreen and dividing it by the time taken for you to burn without a sunscreen. For example, if you burn in 300 minutes with a sunscreen and 10 minutes without, then the SPF of that sunscreen is 300/10 ie. 30. However, sunscreens should not be used to prolong your time in the sun, as exposure still leads to suppression of your skin’s immune or surveillance system.
  2. What does broad spectrum mean? A sunscreen labeled ‘broad spectrum’ provides protection against both ultraviolet A (UVA) and UVB rays. When sunlight hits your skin, it is absorbing both UVA and UVB rays. Whilst UVB rays are the main cause of sunburn, UVA rays can prematurely age and wrinkle skin. Both contribute to skin cancer.
  3. What does the plus (+) sign mean? This means that the SPF is higher than the number shown. In the 2012 Australian standard for sunscreens, the plus sign for SPF50+ means that the SPF is significantly higher than 50. To qualify for a 50+ rating the test results must be 60 or higher.
  4. What does ‘water resistant’ mean? Water resistance is measured by determining the SPF measurement after a period of water immersion claimed by the product. The maximum water resistant claim period of 4 hours is only allowed for products which have SPFs of 30 or more after immersion in water. These are designed to be used while swimming, surfing or participating in other water sports. They still need to be reapplied regularly due to being worn or rubbed off, such as when towelling dry.
  5. How should I apply sunscreen? Apply sunscreen at least 20 minutes before you go outdoors to give time for the sunscreen to be absorbed. Apply liberally to all exposed skin and reapply every 2 hours, even if you don’t sweat or go in the water. Use at least 1 teaspoon for each limb, front and back of the body and half a teaspoon for the face, neck and ears. You should apply one cupped adult hand (30-40 ml or the rough equivalent of a shot glass) of sunscreen for an adult body. If you have small children, apply the sunscreen before you put on their clothes or swimmers to ensure you don’t miss any spots. However, for children you are better off buying a hat and clothing that deflects UV rays (rash shirts).
  6. Are moisturisers or cosmetics containing sunscreens enough? Moisturisers or foundations that contain sunscreen provide skin protection for short outdoors bursts – but that’s it. If you’re planning to spend a significant amount of time outdoors then these alone don’t cut it.
  7. Should I apply moisturiser or sunscreen first? Although there is some debate about this depending on the type of sunscreen, the vast majority of medical experts recommend that sunscreen be applied as the final step in your daytime skin care regime.  Any skincare product applied over a sunscreen dilutes the sunscreen’s effectiveness to some degree. However, the order doesn’t matter as much as thorough, adequate application. If applying foundation, wait 3-5 minutes after sunscreen application and apply using a smooth, gentle motion.
  8. Fake tans do not provide sun protection. Fake tans are great for replicating a sun-kissed glow, but just because the skin looks darker doesn’t mean it’s any more protected from the sun. Apply a sunscreen as you normally would.
  9. Don’t buy a product that combines a sunscreen and an insect repellent. Sunscreen should be reapplied frequently, but insect repellents should not. Buy separate products and apply them separately.
  10. Get rid of old sunscreen. Just like most creams, sunscreens have a shelf life. Theoretically it’s good until the expiration date, but that’s only if it hasn’t been exposed to any extreme heat. Ideally sunscreen should be kept out of direct sunlight and below 48 degrees. If you notice your sunscreen has split, changed colour or smells weird then ditch it!