Teacher Background Information
The electromagnetic (EM) spectrum is the name given to a group of radiation types which originate from
the sun. All the radiation types consist of streams of photons which travel in a wavelike pattern and move at
the speed of light. Each type of radiation contains photons which have a certain amount of energy and a
particular wavelength. The electromagnetic spectrum consists of radio waves, microwaves, infrared, visible
light, ultraviolet light, x-rays and gamma rays. The energy associated with these radiation types ranges from
radio waves, which have the least energy, to gamma rays, which have the most energy.
Visible light contains wavelengths from 400 nm to 700 nm and is the only type of EM radiation which is
visible to the human eye. Ultraviolet light has wavelengths which are slightly shorter than those of visible
light. Our eyes can't visualize these wavelengths, but they can be absorbed by skin cells and the energy
associated with them can damage DNA in the absorbing cells. Some exposure to UV light is necessary for
good health. The sun is critical in the creation of Vitamin D in our bodies, and it promotes the absorption of
calcium into cells. Prolonged exposure to UV light, however, is detrimental to our health. It can cause
premature wrinkling of the skin, skin cancer and cataracts. There are three types of UV radiation emitted by
the sun—UVA, UVB, and UVC. UVC is the most dangerous of the three. It has wavelengths of 100 –280
nm. It is absorbed by Oxygen and ozone molecules in the stratosphere and none of it reaches the earth's
surface. UVB radiation is absorbed by the upper layers of skin called the epidermis and overexposure can
cause sunburn. UVA radiation penetrates to the lower layers of the epidermis where melanocytes are
triggered to produce the pigment melanin. Melanin causes tanning. The purpose of the melanin is to protect
the skin from burning; however, damage from UV light occurs even before the skin darkens. Deep
penetrating UVA rays can go through the epidermis into the dermis where blood vessels and nerves are
found. It can cause damage to the immune system making it harder to fight off diseases.
UV radiation which reaches the Earth has become more abundant over the last century and continues to
increase. This is due to the thinning of the stratospheric ozone layer. Chlorofluorocarbons (CFCs) have been
implicated in the majority of ozone damage. The CFC molecules lose Chlorine atoms from their structure
which attack and destroy ozone molecules in the stratosphere. With large numbers of ozone molecules
destroyed, thinning of the ozone layer occurs. That lowers its effectiveness in filtering out harmful UV rays.
Since UVA light does not penetrate very far into the skin, the damage it does to the DNA of cells has been
linked to skin cancers which appear in the upper layers of the skin. These skin cancers include basal cell
carcinomas, which are the most common of all skin cancers, and squamous cell carcinomas, which are the
second most common. Eight hundred thousand basal and squamous cell carcinomas are diagnosed annually
in the United States. UVA damage to the dermis is also the main cause of premature aging of the skin.
Deeper penetrating UVB rays can lead to the least common but most deadly form of skin cancer—
malignant melanoma. These are cancers related to the melanin producing cells deep in your skin layers. If
not found and treated early, it can quickly spread from the skin to other body organs. More than 1 million
cases of skin cancer are diagnosed in the United States annually. Higher numbers of younger people are
diagnosed with melanoma than ever before. A 1% decrease in the ozone layer is estimated to cause a 2%
increase in UVB radiation reaching the earth, which can lead to a 4% increase in basal cell carcinomas.
To prevent the damage caused by both UVA and UVB radiation, sunscreens or sunblocks are
recommended. The first commercial sunscreens became available during WWII. At this time, U.S. sailors
used zinc oxide to prevent sunburn. Sunscreens eventually became available to the general public in the
1950s and 1960s. Today, 17 sunscreen active ingredients are approved for use in the United States. Twentyfive are approved in Europe. Sunscreens combine organic and inorganic active ingredients to absorb, reflect
or scatter the sun's rays on the skin. Inorganic active ingredients include Zinc Oxide (ZnO) or Titanium
Oxide (TiO2). They act as a physical block to UV rays and reflect or scatter them off the skin. Organic
active ingredients include octyl methoxycinnamate or oxybenzone which absorb UV radiation, dissipating it
as heat out into the environment. Different ingredients vary in the type of radiation they are best at
protecting against. The majority of sunscreens on the market are specialized to block UVB rays (290–320
nm). These sunscreens include those that contain one or more of the following ingredients: padimate O,
homosalate, octylmethoxycinnamate, benzophenone, octyl salicylate, phenylbenzimidazole, sulfonic acid
and octocyclene. Since no single chemical blocks the full range of UVB wavelengths, a combination of up
to three of these chemicals are typically used to provide wider coverage. Recently, broader spectrum
sunscreens have become available which retain their UVB protection and add protection for UVA rays, as
well (320–400 nm). This would include adding oxybenzone (for shorter UVA wavelengths) or avobenzone
(for longer UVA wavelengths) to the formula. Alternatively, physical sunblocks which contain either TiO2
or ZnO reflect both UVA and UVB rays, thus providing broad spectrum protection. Since they protect over
the entire range of UV wavelengths, they can be the sole ingredient in the sunscreen.
Traditionally, sunbathers have shied away from the inorganic mineral sunblocks containing zinc or titanium
oxides due to their being an opaque white color instead of transparent. Recently, however, zinc oxide and
titanium oxide have been produced on the nanoscale with particle sizes of billionths of a meter. This is
much smaller than the usual particle size of the minerals and, as a result of their smaller size, is transparent
instead of opaque white. Sunscreen manufacturers have used nanosized Titanium dioxide since 1990 and
nanoscale zinc since 1999. Today, there are over 300 sunscreens on the market which contain these
nanosized particles. The ingredients are extremely effective at deflecting the sun's rays off the skin,
therefore, preventing penetration of the UV rays, which not only prevents burning but also any damage to
genetic material of the cells which could lead to cancer. Some studies have shown that consumers who use
sunscreen products that do not contain zinc or titanium are exposed to 20% more UV radiation than those
who do. While zinc and titanium nanoparticles are effective at preventing sunburns and associated sun
damage, there is controversy about the use of these particles in sunscreens. The controversy stems from the
lack of definitive safety data and consumer information on sunscreens that contain these particles, as well as
the lack of requirements to label sunscreens as containing nanosized particles. Some concerns are that the
nanoparticles could be absorbed through the skin of the user into the lower, viable layers of skin cells and
then react in a way which could be unsafe inside the human body when exposed to sunlight. Nanosized
particles are well known to be more reactive than their larger counterparts. These particles are known to
emit free radicals upon absorption of UV or visible light, which could cause damage to the biomolecules
such as DNA inside the cells. In addition, many are concerned about the particles washing off the skin and
entering the environment where they could cause unknown damage.
To answer some of the concerns regarding nanoparticles in sunscreens, the Environmental Working Group
conducted a study of the available scientific literature including 400 peer reviewed studies on the topic of
nanoparticles in sunscreens. They concluded from their review that sunscreens without zinc and titanium
actually have four times as many hazardous ingredients. Some of the ingredients in traditional sunscreens
are suspected to cause cancer or birth defects and have been shown to mimic estrogen in the body which
may have a potential breast cancer link. In addition, 16 peer reviewed studies on the skin absorption of zinc
and titanium nanoparticles showed little or no absorption though healthy skin. On the other hand, octinoxate
and oxybenzone (chemicals found in traditional sunscreens) have been shown to be absorbed through
healthy skin and also to cause allergic reactions in some. As a result, the Environmental Working Group
concluded that zinc and titanium formulas are probably the safest and most effective products on the market
based on available evidence. This is an interesting endorsement as the EWG conducted the review with the
idea that they would not be recommending these products. They, however, only recommended them in
lotion form and not in spray or powder form, as these types may cause inhalation of these nanosized
particles which can produce an inflammatory response due to the high surface area of the particles involved.
In 2000, the European Union approved nanosized titanium for use in sunscreen and concluded that it does
not penetrate the skin and presents no risk of cytotoxicity, phototoxicity or genotoxicity. Nanosized zinc
was not approved by the European Union due to the fact that not enough research could be found on its
safety. In 2009, the Therapeutic Goods Administration (TGA) in Australia conducted an updated review of
scientific literature on the topic of absorption of nanoparticles from sunscreen. It concluded that the weight
of current evidence suggests these particles do not reach viable cells but instead remain on the surface of the
skin which is composed of nonliving cells. In the United States, the FDA has not conducted any studies
about the safety of these chemicals at the nanoscale.
An additional concern about these sunscreen ingredients is their environmental effect when they wash off
skin into water and then enter reservoirs or natural ecosystems. Both zinc and titanium are known to have
strong antibacterial properties. These antibacterial properties could be magnified with nanosized particles
since they have a smaller surface area and are more reactive. In a study which appeared in Scientific
American in March of 2009, which was done at the University of Toledo, it was concluded that nanosized
titanium dioxide molecules reduced the effectiveness of environmental bacteria after less than 24 hours of
exposure. They added varying amount of nanoparticles to water which contained bacteria and found that the
bacteria had significant cell wall damage when the amounts were as small as 10–100 mg/L of the nano
TiO2. In another study done at Utah State University and the University of Utah, beneficial soil bacteria
were shown to be damaged by nanoparticles of silver, copper oxide and zinc oxide, even at very low levels
of exposure. Additional concern comes from the unknown unintended effects of these particles on the
environment. Clearly, more research needs to be conducted before the environmental safety of sunscreen
products can be ascertained.