So let’s dive in see what is in sunscreens and why it is important.
It is the active ingredient that determines how effective is the sunscreen. There are two types of active ingredients found in sunscreens; physical and chemical. Chemical sunscreens are chemicals which absorb the UV light and render it harmless. Physical sunscreens sit on top of the skin and actually block the UV light
There are three major characteristics that we consider in a sunscreen.
1 Effectiveness: how good is the sunscreen is at reducing the amount and type of UV light absorbed by your skin. For UVB, this is measured as SPF but SPF is not a good criteria for measuring how well it protects from UVA. That is because the damage caused by UVB occurs in minutes to hours and can be easily measured as a burn. The damage from UVA occurs slowly over years and is difficult to directly measure. So there is no good measure of UVA blockage. But how effective is a sunscreen is function of the type of active ingredient in the sunscreen.
2 Elegance: How well the sunscreen feels on your skin. An elegant sunscreen feels wonderful and light on your skin. A less elegant sunscreen will feel thick and uncomfortable. The type of sunscreen does have an impact but it is really the inactive ingredients that makes the difference on how the sunscreen feels. High quality ingredients such as moisturizers will be well absorbed by the skin and feel light. Lower quality ingredients will be poorly absorbed leaving a cake like feel.
3 Substantiveness: How well the sunscreen stays on your face. A very substantive sunscreen will stay on even if exposed to water. We call this water resistant. A less substantive sunscreen will not stay on your skin for any length of time. Again it is the inactive ingredients in the sunscreen that really have an impact on how substantive is sunscreen.
There are only two physical sunscreens available today, zinc oxide and titanium dioxide. Both of these are inorganic compounds that sit on the skin and work by physically blocking the penetration of UV light into the skin. For example, the white thick sunscreen that we associate with lifeguards is zinc oxide. The two compounds have many advantages over chemical sunscreens.
Because they don’t absorb UV radiation, physical sunscreens do not break down when exposed to sunlight. For this reason they last longer on the skin. Though if your skin is exposed to perspiration or water, they will wash off as easily as the chemical sunscreens. When participating in active outdoors activity, water resistance is still a necessity.
They are more broad spectrum covering both UVA and UVB though titanium dioxide covers a little less than zinc oxide. In addition, they are not absorbed into the skin so they are non-allergenic. They do not cause skin allergies and are safe for people with sensitive skin.
They do have some disadvantages. First, in their natural state, both zinc oxide and titanium dioxide are a thick white paste. When put on the skin in that state they offer the absolute best protection. But it is not very cosmetically elegant and no one wants to cover their face with a thick white paste.
To deal with this problem, micronized particles of the two compounds were created. These are very very fine particles that will actually blend into the skin and become invisible yet still provide superior skin protection from UV light. Of the two, micronized zinc oxide is the more cosmetically elegant. Unfortunately the process of making these tiny particles is more expensive than routine sunscreens so micronized physical sunscreens tend to be slightly more expensive than routine sunscreens.
Finally, there are some questions about whether the micronized particles can be absorbed into the body and potentially cause harm. Several recent study groups in both the United States and Australia have looked into this and found no evidence of any risk, but this issue is still being investigated. What is known is that their ability to prevent skin cancer and premature aging is much greater than any potential risk.
There are many many different kinds of chemical sunscreens. They have names such as octyl salicylate, octinoxate, avobenzone, octisalate, homosalate, padimate, and many others that have been synthesized. These are chemicals that absorb the UV light and convert into heat which is harmless.
Chemical sunscreens are less expensive to make which can help reduce the cost of a sunscreen. They are very good at blocking UVB light. One can mix and match which ones are put in a sunscreen (most will have more than one chemical sunscreen) to get the exact amount of reduction (effectiveness) desired.
Unfortunately, there are disadvantages to chemical sunscreens. First, the process of absorbing UV light can actually cause them to break down. This is one of the major reasons why it is so important to reapply sunscreen several times a day. The active ingredient will usually not last in the sun. Some of the newer chemical sunscreens have been formulated to combat this very real problem. They are more sun stable and do not break down quite as fast.
Second, they often absorb only one part of the ultraviolet spectrum. In addition, almost all of them (except for avobenzone and its variants) do not absorb UVA. Manufacturers often make up for this by layering many different types of sunscreens in the final product to cover both UVA and UVB.
Third, many of them can cause skin allergies. People with sensitive skin tend to have problems wearing chemical sunscreens.
Finally, questions have been raised about whether some of the actual chemical sunscreen products are actually safe to use. There have been studies that show that some of the chemical sunscreens can cause skin damage. Others may cause hormone suppression and potentially be carcinogenic. This area is still being actively researched.