Skin cancer is a fast-growing epidemic in the United States with greater than 3.5 million new cases diagnosed each year.[1] The incidence has tripled since the 1970s. Exposure to the ultraviolet (UV) rays the sun emits is the single greatest risk factor for developing skin cancer.[2]. The 3 main types of UV rays that the sun emits are known as UVA, UVB, and UVC. Ninety-five percent of the UV radiation reaching earth is UVA rays, which are a great cause of photoaging due to their ability to penetrate deep into the skin. UVA rays are known to induce indirect DNA damage by creating free radicals via reactive oxygen species and decreasing the activity of antigen-presenting cells of the epidermis.[3]. UVA rays are used in tanning booths, can also penetrate clouds and glass. They are prevalent year-round. UVB rays, also known as sunburn rays, have a 290 to 320 nm wavelength and are more associated with skin cancer than UVA tanning rays, which have a 320 to 400 nm wavelength.[4] This is because UVB rays cause direct DNA damage by inducing the formation of cyclobutane pyrimidine dimers and pyrimidine (6-4) photoproducts.[5] The third type of rays, UVC rays, although more damaging to the skin than UVA or UVB, are completely absorbed by the ozone layer, and therefore, do not increase the risk of skin cancer. In addition to directly damaging DNA, UV radiation alters the skin in ways that cause skin immunosuppression that may also lead to skin cancer, although the exact mechanism is unclear.[6]

Skin cancer prevention comes in many forms, including mindfulness, proper clothing, and the use of sunscreen. The primary form of prevention is avoiding excessive exposure to the sun’s ultraviolet radiation. Additionally, patients should discontinue the use of tanning beds.[7] Patients should be instructed to monitor the UV Index, which is an international measurement of the strength of UV rays at a specific time and location. This can be accessed through the weather channel, radio, local newspaper, or the internet. The sun's UV rays are usually the strongest between 10:00 am and 3:00 pm. A great trick recommended by the American Cancer Society is to instruct a patient to measure their shadow in the sun. If their shadow is shorter than their actual height, the sun’s UV rays are at their strongest. Patients should be instructed to either avoid being outside during that time or to increase their use of protective methods against the sun. Wearing UV protective clothing when possible such as a wide-brimmed hat, full-length clothing, and UV-protective sunglasses should always be encouraged. Be mindful of using clothing made of fabric that does not permit the passage of sunlight when held up to the sun. Some clothing is now made with additional sun protection called ultraviolet protection factor (UPF). UPF provides greater protection from UV exposure from the sun. A UPF rating of 30 means that the fabric will only allow one 1/30 of UV radiation to pass through the material. Anything with a UPS rating over 25 is considered very good, and anything over 40 is considered excellent.[8]

Other than avoiding the sun at peak hours and wearing protective clothing, using sunscreen is the single-best habit patients can develop to reduce their risk of skin cancer. Sunscreens come in various types and contain different ingredients that protect against the sun in different ways. Chemical ingredients, such as the frequently used para-aminobenzoic acid (PABA) and cinnamates, absorb solar rays and change UV rays into heat energy. Ingredients like zinc oxide and titanium dioxide work as a physical barrier that deflects UV rays off of the skin. Selecting sunscreens that are labeled as broad-spectrum is important because that indicates that the patient will be protected from both UVA and UVB rays. Zinc oxide and titanium dioxide, aside from creating great barrier protection, are excellent ingredients to look for in sunscreens due to their broad-spectrum UV coverage.[9] An important topic when counseling patients about skin cancer prevention is the sun protection factor (SPF). The SPF number represents the amount of protection from sunburn that sunscreen offers compared to using no sunscreen at all. For example, if a patient’s skin would normally take 10 minutes to burn and the patient appropriately applies SPF 30 sunscreen, it would take him or her 30 times longer (300 minutes) to burn. The American Academy of Dermatology recommends using a sunscreen with SPF 30, which filters out about 97% of UV rays from the sun.[10]

Choosing the right sunscreen for your patient will depend on the patient’s skin type, any allergies the patient may have, and the age of the patient. Sunscreen should be applied 20 to 30 minutes before sun exposure and reapplied every 90 minutes after. There is no such thing as waterproof sunscreen; however, the FDA has approved 3 levels of water resistance based on a product's ability to resist an 80 minute period of water immersion. Sunscreens with a higher water resistance factor should be encouraged with reapplication of sunscreen at least every 90 minutes. This is especially true when involved in water activities. If the sunscreen has a lower water resistance factor, reapplication should be even more frequent.

Skin cancer is more prevalent than all other types of cancer combined. It is estimated that 30,000 people will die from melanoma and nonmelanoma skin cancers in 2018.[11]. Patients should have yearly skin checks to reduce their risk of invasive skin cancers, but may be seen more frequently should the patient have a higher risk of skin cancer. Patients with an increased risk include those with a prior history of skin cancer, excessive sun exposure, skin phototypes I and II, family history of melanoma, genetic disorders with an increased risk of skin cancers, and immunosuppression. Other risk factors include smoking and those with known HIV, HPV, and polyomavirus infections.[12] Detection of actinic skin damage during a skin exam can be treated with field therapy using 5-fluorouracil, ingenol mebutate, imiquimod, or photodynamic therapy with red or blue light.[13]

Many medications are known to increase photosensitivity, which can increase the risk for skin cancer. These medications include but are not limited to tetracyclines (especially doxycycline), thiazide diuretics, sulfonamides, fluoroquinolones, nonsteroidal anti-inflammatory drugs, retinoids, and St. John's wort.[14] Physicians should be intentional about counseling patients on these medications to avoid the sun and to wear sunscreen. Further, a general decrease in immunosuppression by making the previous changes or lower the use of steroids can also decrease the risk of skin cancer.

Increasing research is being conducted on oral agents that can prevent or treat skin cancer. Low-dose capecitabine has been researched for the secondary prevention of nonmelanoma skin cancers in solid organ transplant recipients.[15]. Systemic retinoids, such as acitretin, have also been found to be successful in the chemoprevention of skin cancer in solid organ transplant recipients.[16]. Additionally, vismodegib, a sonic hedgehog inhibitor has been shown to be effective against advanced basal cell carcinomas.[17]

There is some research that suggests that antioxidants and vitamins are helpful for chemoprotection of skin cancer.[18] These may be used adjunctively, but should not be solely recommended because the previous recommendations listed above are more effective. Studied compounds include but are not limited to vitamin A, vitamin C, vitamin E, selenium, fatty acids, and resveratrol. Topical difluoromethylornithine and calcipotriol are also currently being studied for skin cancer chemoprevention.[19]

Outcomes 

Overall, it appears that the rates of skin cancer have increased. This could be due to an aging population, more awareness or due to a shift in lifestyle. Whatever the case, there is now less argument about the use of a sunscreen 24/7 throughout the year. [20] (Level V)