Sunscreen With Nanoparticles—Safety Concerns and English Ivy
Nanoparticles and Sunscreen
Although sunlight is essential for life on Earth, it has its drawbacks. One of these is the ability of ultraviolet light to cause skin cancer. Some form of sun protection is necessary. For many people, this protection consists of sunscreen. Unfortunately, the skin can absorb certain chemicals, including the potentially harmful ones in some sunscreens. An exudate from the English ivy plant may provide a safer sunscreen.
Mineral sunscreens contain either titanium dioxide or zinc oxide. They are often considered to be safer than chemical sunscreens. The minerals give the skin a white appearance, however, which many people find unappealing. To avoid or reduce this whitening effect, many sunscreen manufacturers use the minerals in their nanoparticle form.
Nanoparticles are tiny and behave differently from particles of normal size. Although sunscreens containing nanoparticles are generally considered to be safe, there are some concerns about their effects on our body. English ivy produces nanoparticles that block ultraviolet light and may be safer than the ones produced from minerals.
Nanoparticles are very tiny particles between 1 and 100 nm (nanometres) in diameter. A nanonmetre is a billionth of a metre or one millionth of a millimetre. The millimetre is the smallest division on a metric ruler.
Titanium Dioxide and Zinc Oxide Sunscreens
Sunscreens containing titanium dioxide and zinc oxide are often called mineral sunscreens because both chemicals are found in the Earth. In contrast, chemical sunscreens contain chemicals produced in a laboratory. Mineral sunscreens are also known as physical sunscreens. They act as barriers to dangerous light rays by reflecting and scattering light and are effective sun blocks. In their normal form they appear to be safe and unable to penetrate the skin.
Reducing titanium dioxide and zinc oxide particles to nanoparticle size removes most of their white colour. When chemicals are reduced to nanoparticles, their properties and behaviour change. These changes are often beneficial. Nanoparticles are helpful in medicine, technology, and manufacturing. There are concerns about the effects of some nanoparticles on living things, however.
Can Nanoparticles in Mineral Sunscreen Penetrate the Skin?
Cosmetics companies claim that titanium dioxide and zinc oxide nanoparticles in sunscreens can’t penetrate human skin. They say that the particles form a layer on the surface of the skin instead, thereby avoiding any damage to our bodies, and that any penetration is limited to the stratum corneum. The stratum corneum is the surface layer of the skin. It's composed of dead cells filled with keratin, a protein that prevents water loss from the body.
The majority of the scientific research into mineral sunscreen safety agrees with the cosmetic companies. Most experiments show that healthy human skin is able to prevent penetration of nanoparticles or that the particles penetrate only the outer layer of the stratum corneum. Some experiments have raised questions, however.
Scientists have discovered that long exposure to a titanium dioxide sunscreen allows the nanoparticles to penetrate the skin of hairless mice. It's unclear how applicable this is to human life. Other researchers say that skin damaged by factors such as sunburn, shaving wounds, and blemishes can absorb nanoparticles to a greater depth than healthy skin. They also say that the smaller the nanoparticles, the further they can travel into the skin.
Skin contact with TiO2 is not likely to cause harm due to minimal penetration through the skin under normal use conditions. However, information on long-term use of sunscreens containing nanoparticles on hairy, damaged, flexed or aged skin is limited.— Australian Government Department of Health
Effects of Titanium Dioxide and Zinc Oxide Nanoparticles on the Body
Titanium dioxide in the form of a dry powder is considered to be a possible carcinogen (cancer causer). The public doesn't encounter the chemical in this form in sunscreens, however.
There are two main areas that are being investigated in relation to sunscreen nanoparticle safety: the production of inflammation and damage to DNA.
- When titanium dioxide nanoparticles are injected under the skin of mice, they have been found to cause inflammation.
- When titanium dioxide or zinc oxide nanoparticles react with ultraviolet light, they produce reactive particles that can damage DNA. DNA, or deoxyribonucleic acid, is our genetic material. Sunscreen manufacturers use coated nanoparticles, however. The coating material prevents the nanoparticles from reacting with light.
- Not all nanoparticle coatings are equally effective. In addition, researchers are trying to discover whether some coatings are removed by the chlorine in swimming pools, as research suggests.
- Some scientists say that we should be investigating the effects of sunscreen nanoparticles that enter the lungs or digestive tract.
At the moment, there seem to be fewer safety concerns about zinc oxide nanoparticles than titanium dioxide ones.
The American Cancer Society says that it's important that we choose a sunscreen that we are reasonably comfortable with and use it regularly. The society says that skin cancer is a more serious concern than the possible danger of sunscreens.
Does the safety of sunscreens worry you?
A Potentally Safer Sunscreen From English Ivy
Scientists at the University of Tennessee have found that ivy nanoparticles block ultraviolet light from the sun much better than conventional sunscreens containing nanoparticles. In fact, they say that an ivy sunscreen may be four times better than a mineral sunscreen at protecting us from the dangers of sunlight. In addition, the ivy particles are sticky and should adhere to skin more effectively.
When they tested isolated cells, the scientists found that the English ivy particles were not toxic to the cells, while titanium dioxide nanoparticles showed significant toxicity. In addition, the researchers found that the ivy particles could be broken down by protein-digesting enzymes, which suggests that they would be biodegradable in the human body.
The researchers also suggested—but didn’t prove—that the ivy particles would be unlikely to penetrate skin because of their size. Another advantage of the ivy sunscreen would be the fact that it could be almost colourless, depending on the carrier liquid.
Identifying English Ivy
English ivy is an attractive garden plant and wall covering or a noxious weed, depending on where it's located and one's point of view. The plant grows aggressively and can be invasive in some habitats. Its vertical stems form adventitious roots that enable the plant to attach to surfaces.
The English Ivy Plant
English ivy (scientific name Hedera helix) is a popular evergreen plant in gardens. It grows fast and is a great climber. Rootlets extend from ivy stems to attach them to tree trunks and walls. These rootlets produce a yellow, adhesive liquid that not only enables ivy to cling to vertical objects but also contains nanoparticles which can block ultraviolet light.
The English ivy plant is native to Europe and Asia but has been introduced to other parts of the world. It can grow in the shade created by trees and is therefore a popular ground cover in dark areas. It also grows well when exposed to full sunlight. Ivy can form an attractive coat on the walls of houses and is able to climb as high as 50 meters (164 feet) in a favourable habitat. However, the plant needs to be trimmed frequently since its growth can quickly get out of control. When it escapes from gardens it’s often regarded as a weed and an invasive species.
Juvenile ivy leaves have three to five lobes, but adult leaves are not lobed. Instead, they are oval and have a pointed tip. The small flowers occur in clusters and have a green-white color. The fruit is a black, berry-like structure.
English Ivy Nanoparticles
A new sunscreen with a safety profile that most scientists accept would be very useful. English ivy might provide such a sunscreen.
The yellow exudate containing ivy's nanoparticles is produced by its adventitious roots. Adventitious roots are those that are produced in an unusual location, such as from an above-ground stem. The ones produced by ivy are short and are known as rootlets. The exudate is released by the fine hairs covering the rootlets.
Ivy nanoparticles have a diameter of 60 to 85 nm and are generally larger than those in mineral sunscreens. Mineral sunscreen nanoparticles come in a range of sizes but may be as small as 20 nm in diameter.
Testing a New Sunscreen
As exciting as the University of Tennessee discoveries are, more research needs to be done. An English ivy sunscreen has to be created and then tested, which doesn't seem to have happened yet. The possibilities are exciting, though. When an investigation has been established and finished, we may have a new, very effective, and safe sunscreen.
- Smijs TG, Pavel S. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnology, Science and Applications. 2011;4:95-112. doi:10.2147/NSA.S19419.
- "Depletion Of The Protective Aluminum Hydroxide Coating In TIO2-Based Sunscreens By Swimming Pool Water Ingredients." Environmental Protection Agency. https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=234786 (accessed August 16, 2017).
- University of Tennessee at Knoxville. "Nanoparticles in English ivy may hold the key to making sunscreen safer and more effective." ScienceDaily. www.sciencedaily.com/releases/2010/07/100719162955.htm (accessed August 16, 2017).
© 2011 Linda Crampton