The sun; the almighty sun. The first dwellers of Planet Earth were so impressed by the sun´s magnificence that they started worshiping it as one of their most beloved gods. Who wouldn't feel dazzled by the energy emitted by the sun? That energy, composed of photons, is what makes the existence of every single living being possible. Sunlight represents life, love, and hope. It goes without saying that the radiation produced by the sun has its own share of pitfalls.
UV Light Family: Technical Definitions and Explanations
We previously mentioned that photons are responsible for the sun´s energy. These light particles vibrate as they move, thus creating energy waves. The term wavelength refers to the distance between two energy crests. There are many wavelengths in Nature and their radiations are inversely proportional to their energy. This means, believe it or not, that more energy is produced by shorter wavelengths. Nanometers are the units of measurement of wavelengths and one unit is equal to one billionth of a meter (1/1.000.000.000 m). A nanometer is so tiny that it is almost impossible to visualize it; it is like a super ultra mini flea.
Why are we sharing this uber technical data? Because ultraviolet light is a type or radiation emitted by the sun within the 100 and 400 nm wavelength and is subdivided as follows:
- UVA: or ultraviolet A; covers the wavelength range between 320 and 400 nm. They are also known as the aging rays as they can penetrate deep down into the dermis and damage collagen and elastin fibers. They rarely cause dermis but have been linked to skin cancer.
- UVB: or ultraviolet B; covers the wavelength range 280 and 320 nm. Their intensity is greatly influenced by time of the day, season, and location. UVB reach their peak between 10 AM and 4 PM (Daylight saving time). They are especially intense at high altitudes and on reflective surfaces such as snow, which bounces back up to 85% of the rays. UVB is known as the burning rays. They do not penetrate as deep as their UVA counterpart —they remain in the epidermis— and are responsible for producing the precious vitamin D.
- UVC: or ultraviolet C; covers the wavelength range between 100 and 280 nm. They are the most dangerous of all UV rays, but the good news is that they do not reach the Earth's surface as they are absorbed by the ozone layer. Well, sort of, as the increasing emissions of CFC (chlorofluorocarbons) have caused the ozone layer to decrease approximately 0.5% every year. UVC rays have powerful antibacterial properties, and an artificial form is still being used in sterilizers.
Now that you are familiarized with the UV light family, let´s review a few more concepts that are crucial for sun protection.
Sun Protection Factor (SPF): What does it mean?
Sun Protection Factor is a measure that indicates how long it takes for UVB rays to produce redness of the skin (erythema) . SPF only measures UVB protection, it does not rate how much protection you get from UVA rays. This is why SPF is considered an imperfect system for measuring UV skin damage.
UVA radiation is measured using other methods like the Persistent Pigment Darkening (PPD), the Boots Star Rating, and COLIPA. The sun protection factor (SPF) ranges from a value of 2 to 100. The higher the SPF, the greater the length of protection/effectiveness provided by sunscreen. As demonstrated below, the actual proportion of UVB rays screened by the different Sun Protection Factors does not differ significantly:
- SPF 15 blocks 93% UVB rays
- SPF 30 blocks 96.7% UVB rays
- SPF 50 blocks 98% UVB rays
- SPF 100 blocks 99% UVB rays
A specific SPF allows you to expose your skin to UVB radiation X number of times (the factor of your sunscreen) longer without burning your skin than when you do not use sunscreen at all. For instance:
5 minutes (the time it takes for your skin to develop erythema sans sunscreen) x 50 (SPF of a sunscreen) = 250 minutes (4 hours and 10 min) of protection.
This is the equivalent of the SPF but for UVA rays and based on the Persistent Pigment Darkening (PPD) method developed in Japan. It is more common to see this rating on Asian and European sunscreens. The higher the PA rating, the more protection a formula will provide as seen below:
PA+ Some UVA protection
PA++ Moderate UVA protection
PA+++ High UVA protection
PA++++ Extremely high UVA protection
Boots Star Rating: The Final Categorical Rating
This is an in vitro method that describes the UVA/UVB protection ratio and was designed by The Boost Company back in 2011. Although it measures UVB, most companies use it to inform customers about the level of UVA shielding offered.
|MEAN UVA/UVB Ratio||Star Rating Category||Star Rating Designation|
|0 to 0.2||-||No Claim|
|0.21 to 0.4||*||Minimum|
|0.41 to 0.6||**||Moderate|
|0.61 to 0.8||***||Good|
|0.81 to 0.9||****||Superior|
|0.91 and above||*****||Ultra|
3 Types of Sunscreen: What is the Difference?
Sunscreens are topical products that shield the skin from the sun's detrimental rays by absorbing, reflecting, and/or scattering UV rays when applied to sun-exposed skin. They significantly lower the risk of skin cancer, photo-aging, photosensitivity as well as the development of other sun-related lesions. They come in various forms such as creams, lotions, gels, sticks, sprays, lip balms, and mineral makeup. Based on their composition they can be classified as:
- Chemical sunscreens: organic molecules that work by selectively absorbing sun radiation (UVA A, UVA B), converting it to heat, and then releasing it. PABA (para-aminobenzoic acid) and its derivatives (such as cinnamates), avobenzone, benzophenones, oxybenzone, octocrylene, and salicylate are among the most commonly used chemicals.
- Physical sunscreens: are formulated with inorganic compounds, mainly titanium dioxide and zinc oxide, that shield the skin from sunlight by reflecting, scattering, or absorbing it.
- Biological filters: they are not sunscreens or UV filters per se, but they can neutralize the negative effects of solar radiation (premature aging and formation of free radicals) thanks to their antioxidant effect. Among the most utilized biological filters are green tea extract, vitamin E, sesame seed oil, avocado oil, wheat germ oil, shea butter, and raspberry oil.
There are other terms to be mindful of when purchasing a sunscreen:
- Broad Spectrum Sunscreens: prevent sunburn and minimize tanning by a barrier that filters wavelengths from 290 to 770 nm (UVA, UVB, and Visible light).
- Pediatric Sunscreens: these are formulas specifically created for children, as they are more vulnerable to sun damage.
- SPF+: this means that its protection goes beyond the value specified on the level, like SPF 30+ (it would reach, then a minimum of SPF 40).
- Water-resistant: is a sunscreen that maintains its SPF level after 40 minutes of exposure to water.
- Very water-resistant: is a sunscreen capable of maintaining its SPF level after 80 minutes of water exposure
Global UV Index: Exposure Category & UVI Range
The UVI was developed by WHO in collaboration with several international organizations. The UVI measures the intensity of UV radiation that reaches the Earth's surface. It functions as a tool that clearly indicates the ability of UV rays to produce skin lesions. The main purpose of the UVI is to educate people on the damaging effects of the sun so that they can adopt protective measures against it. Based on the UVI index, you can determine how much protection you need as well as how safe it is to stay outdoors (and for how long). Other people use it for vitamin D production because a high range is required for this purpose.
|EXPOSURE CATEGORY||UVI RANGE|
|MODERATE||3 TO 5|
|HIGH||6 TO 7|
|VERY HIGH||8 TO 10|
Taken from 
Sunscreen Selection: Characteristics To Keep In Mind
- Phototype* of the individual. Please refer to our Fitzpatrick Classification Scale article.
- Age: the skin of children is more vulnerable to sun damage than the skin of adults
- Chemical composition of the sunscreen
- The cosmetic form of sunscreen: lotion, gel, spray, etc.
- Method of application
- Frequency of re-application
- UV Index
- Altitude: the higher the altitude, the stronger the intensity of radiation
- Obliquity: determines the angle of incidence of solar rays on the Earth's surface
- Latitude: the obliquity of solar rays differs every season
- Climate: clouds and humidity absorb radiation
Surface: the reflection of the solar rays varies according to the surface: Fresh snow reflects from 75-95% of radiation; sand, 35 - 45 %; water, 5 – 10 %, grass 3 - 5%, etc.
Rosafa's Tips For Maximum & Beneficial Sun Protection
- Go for a physician sunscreen since these are non-toxic, stable, sustainable, and are suitable for even the most sensitive skin types. You will get an added benefit if these also contain antioxidants.
- The cosmetic form will depend on your skin type. However, we've noticed that lotions/creams are better at guaranteeing the proper application of sunscreen. There are some lightweight options in the market that are suitable for oily complexions too.
- Physical sunscreens, when applied, might leave a white cast, but you might be able to camouflage it if you choose a tinted formula or layer makeup on top.
- You need to apply 2 mg/cm2 of sunscreen to secure proper protection. In an adult, this translates into 1 ounce (2 tablespoons) for both the face and the body, per application. So, for the face and neck that is approximately 1/2 to 1/3 teaspoon. Use the rest for the body.
- Apply sunscreen on properly moisturized skin. Evenly distribute the sunscreen on the palms of your hands and then press them against the skin until you have covered all the exposed areas (with the previously recommended amount). Do not forget to protect your lips with a balmy formula.
- Reapply sunscreen every 2 hours. It may be necessary to reapply it before if there was some rubbing, sweating, or swimming involved.
- Pick a water-resistant formula if your skin is going to come into contact with water.
- SPF: minimum 30 for dark complexions and 50 for fair ones
- PA Rating: minimum PA+++ for dark complexions and PA++++ for fair ones
- Boots Star Rating: minimum *** for dark complexions and **** for fair ones
- UVI: try not to stay outdoors longer than 40 minutes with a high UV range. If you have no option, opt for a higher SPF/PA or Boots Star Rating than usual. Most weather apps show the UV Index.
- Indoors protection is only needed if you are staying close to a window because they can´t block UVA radiation.
- Wear protective clothes: broad-brimmed hat, sunglasses, etc. Some companies are now offering sun protective clothing made with special fabrics that contain UV absorbers (based on the Ultraviolet Protection Factor). As a rule of thumb, fabrics that are densely woven and that have brighter colors are more protective.
- If you must wear makeup, we recommend reapplying the sunscreen with a sponge and using the dotting technique (saturate the sponge with the sunscreen and then dot). You can use a different cosmetic form for this purpose (powder, compact makeup with SPF). Just keep in mind that you will still need to follow the 2 mg/cm2 rule. You can carefully touch up your makeup afterward.
- Maximize your intake of antioxidants: carrots, beets, yams, berries, grapes, leafy vegetables, tomatoes, watermelons, matcha tea, you name it. Make this a part of your dietary regime and you will quickly notice how your inside-out UV protection system is boosted.
Properly protecting yourself against UV radiation requires a little bit of education and effort, but it is absolutely essential to keep your skin free from cancer, photoaging, and other related conditions. We are confident that the information that we have presented here will help you maintain healthy skin and befriend the almighty sun. To learn more about your skin, make sure to follow us on
 Vinson, T. (2021). Skinformation: A Clean Science Guide to Beautiful Skin. New York: Wiley.