During the summer, when the sun is at full strength, many choose to shield themselves from the sun by staying inside, covering their skin, or applying suntan lotion. But the damaging effects of the sun persist throughout the year, and some precautions may not be as adequate as we think.
UVB and UVA: Differences and Effects
Ultraviolet B (UVB) radiation has a shorter wavelength than UVA and more energy. This shorter wavelength means clouds or windows more easily block it. Most UVB radiation is absorbed by the atmosphere before reaching Earth. Thus, its intensity peaks during midday and wanes during mornings, evenings, or winter in regions further from the equator.
UVB is absorbed in the skin in the top layer, but the higher energy causes more damage. This can cause sunburn and directly damage DNA, making it the primary cause of skin cancers.1
With its sunburn and cancer effects, more measures are available to track and stop UVB. The Sun Protection Factor (SPF) rating on sunscreens reports how long a sunscreen will prevent skin reddening from sunburn. The hourly UV Index reported on many weather apps is primarily based on the amount of UVB radiation at that time.
With a longer wavelength and less energy, Ultraviolet A (UVA) radiation is the much more common form of radiation. About 95% of UV radiation reaching the Earth is UVA. Unlike UVB, UVA traverses the atmosphere, clouds, and windows readily. It also penetrates deeper into the skin, inducing the body to produce more pigmentation, making UVA primarily responsible for tanning.
Due to its ease of passing through the atmosphere, UVA is more prevalent in the morning and late afternoon and winter. At about the latitude of New York City, UVB is reduced to a fourth of the summer amount, but UVA is half as much as summer2 in addition to persisting earlier and later in the day.3
Because of the lower energy of UVA, it doesn’t directly damage DNA, but it can cause other chemical reactions that contribute to skin cancer by damaging DNA indirectly.
Sunscreens that protect from UVA, as well as UVB, are called “Broad Spectrum.” For a specific rating of UVA protection, look for the PA rating (Protection Grade from UVA), which has four stages, +, ++, +++, or ++++. The highest rating of PA++++ means it delays suntanning by over 16 times. Developed in Japan, PA ratings are commonly used in Asia and Europe but less in the US.
UVA is also the main culprit behind photoaging, including wrinkles and other aging skin signs. Protecting your skin from UVA is critical to maintaining young, unaging skin. Contrary to UVB, which can be dodged by staying out of direct sunlight or wearing a high-SPF sunscreen around noon in summer, UVA protection requires a more comprehensive approach, including sunscreen throughout the day, even indoors or during winter.
Suntan Lotions: Navigating the Options
Recognized by their characteristic white sheen, mineral lotions primarily employ Zinc Oxide or Titanium Dioxide. They offer immediate protection upon application. However, a Consumer Reports study4 revealed that their actual protection is much less than the labeled rating, ranging from just over half down to, more commonly, a quarter or fifth of the label.
In contrast, chemical sunscreens showcase superior performance. While they provide more consistent protection, they need a head start to be effective. Applying them a minimum of 15 minutes before sun exposure is advisable. These sunscreens can penetrate the bloodstream, and research on their long-term effects is ongoing.
While there’s only one sun, the effects of UVB and UVA are different and require different measures for protection. UVB causes sunburns and skin cancers and is primarily an outdoor, summer, and mid-day risk. Stay out of the sun, wear a strong SPF chemical lotion, and reapply every two hours when the UV Index is high.
UVA causes suntans and ages your skin and is more present from dawn to dusk, in winter and summer, in cloudy weather, or through windows. Wear broad-spectrum protection or high PA-rated sunscreen daily to avoid its effects.
Know the kinds of UV radiation and how to handle them to save your beauty and health from the sun!
Do sunscreens harm coral reefs?
Yes, two chemicals in sunscreens, oxybenzone and octinoxate, have been flagged for potentially damaging coral reefs. Both are prohibited in Hawaii. As for other chemical or mineral sunscreens, their impact on reefs remains under study.
Are there any chemical sunscreens that are unhealthy?
It has been found that chemical sunscreens are absorbed in the blood, and the FDA is currently requesting additional safety information regarding this. For now, it’s clear that the risks of not wearing sunscreen greatly outweigh other health effects.
Are spray sunscreens effective?
Spray sunscreens require more care in application. There have been recalls of spray sunscreens from a potential carcinogen called benzine, which wasn’t an ingredient but was found as a contaminant in some spray sunscreens. Also, the FDA has requested additional study on the possible effects of inhaling sunscreen.
Will using daily sunscreen prevent me from getting Vitamin D?
Research from Australia shows that even with regular broad-spectrum sunscreen use, blood vitamin D levels remain within the normal range.5 It seems that adequate vitamin D is available from foods or areas uncovered by sunscreen.