By Philip Shapiro, MD and Alicia Sigal, MD, Board-certified Dermatologists and Dermatopathologists
Summer is here, which for many people means more time in the sun. While the sun has beneficial effects, too much exposure can be damaging to the skin, not only because of its causal roles for skin cancers such as squamous cell carcinoma, basal cell carcinoma, malignant melanoma, and Merkel cell carcinoma, but also because it gives rise to the much more common actinic keratosis (often perceived as a red, rough spot on the face or dorsal hands), which is a non-obligate precursor of squamous cell carcinoma. Furthermore, it contributes to solar lentigines (sometimes referred to as age or sun spots), dyspigmentation, telangiectasias, and wrinkles, which for some are a significant cosmetic concern. Much of the damage caused by sunlight is attributed to DNA’s susceptibility to alteration by ultraviolet light, which can be divided into ultraviolet A (UVA, wavelength 320-400 nanometers) and ultraviolet B (UVB, 280-320 nanometers); sunlight also produces UVC, which is shorter wavelength than UVB and capable of damaging skin but is filtered out by the Earth’s atmosphere before it reaches the earth’s surface. While UVB is primarily responsible for producing erythema (sunburn), UVA’s longer wavelength enables deeper penetration into the skin and is thought to be primarily responsible for changes to collagen and elastin in the dermis, contributing to wrinkling. Also, unlike UVB which is filtered by glass, UVA can penetrate the glass of car and house windows. An individual’s risk of cutaneous adverse effects from the sun’s rays is proportional to the amount of ultraviolet exposure (generally accumulating over years such as occurs in outdoor workers like farmers) and how light one’s skin is–the more natural melanin in the skin (i.e., the darker the skin), the more innate protection one has against ultraviolet’s damaging rays. While staying indoors all the time would prevent sun damage to the skin, most of us enjoy the psychological benefits from being outdoors, so the key is to learn how to balance being outdoors while practicing safe sun. This does not mean using a tanning bed, which has been linked to non-melanoma skin cancer and melanoma. Rather, it involves a combination of controlling the amount of direct sunlight we receive, wearing protective clothing, and the use of sunscreen.
One way to control the amount of direct sunlight we receive is to plan outdoor activities when more of the sun’s rays are filtered by the atmosphere, i.e., to avoid being outdoors midday—the sun’s UVB rays are strongest between 10 am and 4 pm EDT in the summer in Connecticut (note that this is a guideline; it’s better to be out at 9:30 am than 10:30 am, but it’s also better to be out at 10:30 am than at noon). Additional protection can be gained by the use of shade, e.g., by umbrellas, awnings, or trees. Don’t be fooled into thinking that clouds will provide strong protection—while they do offer some benefit, they allow most UV rays to get through. Another way to lessen the amount of direct sunlight is with protective clothing. Wearing a hat is a no-brainer; broad-brimmed hats that cover the ears are better than baseball-style caps, though the latter is better than nothing. Covering the body with clothing is also beneficial. A T-shirt provides some protection, but there are better options from clothing companies that use tighter weaves that still remain lightweight and breathable, providing more protection and comfort while covering sun-exposed limbs; some of these clothes also come with sun protection ratings. If in a swimming environment, use of a cover-up, swim shirt, or rash guard can reduce ultraviolet exposure.
In addition to sun-avoidance and protective clothing strategies, dermatologists recommend use of a sunscreen applied to the skin. The American Academy of Dermatology advises use of sunscreens that meet 3 criteria: SPF (sun protection factor) of at least 30; broad spectrum (UVB and UVA) protection; and water resistance (which provides better protection on wet or perspiring skin). The SPF number can be thought of as the reciprocal of the fraction of UVB rays that are not blocked by the sunscreen. An SPF of 30 means that 1/30th of the UVB rays will not be blocked. In other words, if it would take 10 minutes of sun exposure to produce erythema (redness/sunburn) without use of a sunscreen, it would take 300 minutes to develop the same erythema with the use of an SPF 30 sunscreen (Tip: the erythema one gets from the sun does not reach its maximum until many hours after the sun exposure has occurred, so if you are not red after 10 minutes, you still could be quite red the next day). Another way to think of this is that an SPF of 30 blocks about 97% of UVB rays, an SPF of 50 blocks 98% of UVB rays, and an SPF of 100 blocks 99% of the rays. This is why it is said that using an SPF above 30 does not provide significant additional blocking; however, if you will be exposed for a long time or have light skin and burn easily, an SPF above 30 may be of practical usefulness. In the early days of sunscreen development decades ago, the focus was on blocking UVB that causes sunburn, but with the later understanding that UVA also produces damage, sunscreens should be broad-spectrum and provide protection against both UVB and UVA.
Sunscreens can be divided into 2 general categories, based on their ingredients: physical, which physically block the UV rays (e.g., with minerals zinc or titanium) and chemical, which absorb the UV rays (these are also referred to as organic because of their chemical structure and include molecules such as PABA and its derivatives; benzophenones including oxybenzone and avobenzone; octocrylene; cinnamates; and salicylates including homosalate and octisalate). The chemical sunscreens are in greater use today, in part because they are easier to apply and tend to provide greater protection, and they are less likely to leave a white residue on the skin; however, the physical sunscreens are gaining in popularity as formulations are developed that are cosmetically more acceptable. Furthermore, compared to chemical sunscreens, physical sunscreens are less allergenic, are generally of less concern about possible systemic effects from absorption, and are less harmful to coral reefs.
While the SPF of a sunscreen is important, proper use of the sunscreen may be at least as important, as most users fail to apply enough. One ounce (the size of a shot glass) is recommended to cover the entire body. Another way to think about this is to apply a teaspoon per body part: head/neck; each arm; each leg; front of torso; back of torso. If you are in the sun, reapplication every 2 hours is recommended (especially for chemical sunscreens, which become degraded after exposure to ultraviolet light, unlike mineral sunscreens). Reapplication after swimming or heavy sweating is also advised.
Here are a few additional tips about sunscreen use. While makeup may have an SPF number, it is generally not considered a substitute for sunscreen use, so it is best to apply a sunscreen first, allow it to dry, then apply makeup over that. The American Academy of Dermatology recommends avoiding sunscreen use in those less than 6 months old (sun avoidance is preferable), but if sun cannot be avoided, a blocking type of sunscreen is preferred over an organic one. Another tip—if you find it difficult to be meticulous about sunscreen use, at least focus on protecting your face and the backs of your hands, because these are the most cosmetically sensitive areas and also present more difficulties in treatment (removing a skin cancer from the back is much less complicated than removing one from the ear). If you would like advice on which specific sunscreen to use, you could check the ratings in Consumer Reports July/August 2025 issue (probably the least biased source); look for the Skin Cancer Foundation’s Seal of Recommendation for a sunscreen; or consult the Environmental Working Group (EWG) recommendations (the latter’s may be the most restrictive and have been described as showing some bias but may be a good source for those that are particularly wary of potential safety issues—see below).
This blog post would not be complete without addressing some of the controversies around sunscreens. One concerns the question of inadequate vitamin D levels if sun exposure is curtailed. However, adequate vitamin D levels can be obtained with a healthy diet, with oral supplements if needed. Another concern is the systemic absorption of ingredients. Chemical sunscreens can be absorbed and detectable in plasma. While there has not been shown to be any harmful effects from this, it does not mean that they cannot occur. This is why the FDA designation “generally safe and effective” has been assigned to physical sunscreens but not to chemical ones. What about spray sunscreens, which have fallen out of favor? Concerns include tendency to inadequate application when applied via spray, as well as possible inhalation hazard and the recently-noted benzene contamination in some formulations. Many (but not all) of the contaminated sunscreens have already been recalled by the manufacturers. If spray sunscreens are to be used, suggestions for application include spraying into the hands and then applying to the skin, and using common sense measures to avoid inhaling the spray.
In summary (please pardon the pun), it is possible to enjoy the benefits of sunlight while protecting the skin, using an individually tailored approach based on your risk factors, utilizing the strategies of minimizing direct sun, wearing protective clothing, and sunscreen use. While there may be some theoretical downside to sunscreen use, the known benefits (reduction in actinic keratoses, skin cancers, and photoaging) likely far outweigh the concerns, and sunscreen use is strongly recommended for individuals whose skin tends to show visible evidence of DNA damage after exposure to sun (i.e., tanning, which is a reaction to damage, and especially burning). Finally, remember to wear UV-protective sunglasses for your eyes, and lip balm with an SPF of 30 as well.
