Video: Reason for Adding Nanoparticles to Sunscreens

Nanoparticles are used in sun cream. Which of the following reasons is not an advantage of adding nanoparticles to sun creams? [A] Nanoparticles in sun creams provide better protection against UV rays. [B] Nanoparticles in sun creams give better skin coverage. [C] Nanoparticles in sun creams result in a transparent liquid. [D] Nanoparticles in sun creams are absorbed deeper into the skin and provide longer protection. [E] Nanoparticles in sun creams may be washed away into the environment.

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Video Transcript

Nanoparticles are used in sun cream. Which of the following reasons is not an advantage of adding nanoparticles to sun creams? (A) Nanoparticles in sun creams provide better protection against UV rays. (B) Nanoparticles in sun creams give better skin coverage. (C) Nanoparticles in sun creams result in a transparent liquid. (D) Nanoparticles in sun creams are absorbed deeper into the skin and provide longer protection. Or (E) nanoparticles in sun creams may be washed away into the environment.

Nanoparticles are particles that are 1 to 100 nanometers in size. Sun creams generally contain particles of titanium dioxide, which are there to absorb UV light and help prevent sunburn. Our job is to identify which of the five statements is not an advantage of adding nanoparticles of titanium dioxide instead of large particles to sun creams.

The first statement suggests that nanoparticles in sun creams provide better protection against UV rays than larger particles. It’s hard to see how the size of particle is going to affect how well it absorbs ultraviolet light, so I’m going to come back to this statement later.

The second suggestion is that nanoparticles in sun creams give better skin coverage. On first look, it looks like big particles will cover surface just as well as small particles. But skin is actually quite rough and uneven. Smaller particles will fit into the holes and gaps much better than bigger particles. And you’ll use a smaller massive particles to cover the same surface area. And it’s a clear advantage that nanoparticles give better skin coverage in sun creams than larger particles. So, this is not our answer.

The next suggestion is that nanoparticles in sun creams result in a transparent liquid. Large pieces and large particles of titanium dioxide are white. But nanoparticles are smaller than the wavelength of visible light, and titanium dioxide nanoparticles appear colorless in a thin film or in solution. So, nanoparticles in sun creams don’t turn the liquid white, which, from a commercial perspective, is a bonus because people don’t want white streaks on their skin when they apply sun cream.

The next suggestion is that nanoparticles in sun creams are absorbed deeper into the skin and provide longer protection. Nanoparticles of titanium dioxide can get into the gaps in your skin much, much deeper than larger particles and, therefore, stick around longer and provide longer protection. Therefore, this too is true. And we can see how being absorbed deeper, providing longer protection, and giving better skin coverage would make nanoparticles in sun creams provide better protection against UV rays than larger particles.

This leaves us with the final suggestion that nanoparticles in sun creams may be washed away into the environment. On first glance, this does look like an advantage. You don’t want to have sun cream kegged to your skin after you come home from the beach. However, while large particles of titanium dioxide are considered safe, it’s not been proven that nanoparticles are safe in all situations. It may be that we find it damages the environment in ways we haven’t yet understood. So, until we know better, we should be wary about putting nanoparticles into the environment.

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