It is that time of year when my tan lines begin to show. No, I am not talking about the ones on my shoulders, I am talking about the ones from my Birkenstock® sandals. Even before my whole world became filled with lower extremity dermatology, I have always been emphatic about wearing sunscreen. However, I, too, from time to time have fallen into the majority of people who forget to coat the surfaces of their feet with SPF 15 or higher.
Why are the feet the forgotten place? Do we think wearing our sandals will give us some sort of protection? Do we think burying them in the sand will keep the sun’s harmful rays away? Well, neither of those is true of course. Are we so concerned about our faces and upper extremity that we just think the feet and legs will continue to be the place where the sun does not shine? Perhaps.
As most of you know from your own experience or from your patients, sunburn is a real occurrence on the lower extremity. Burns on the plantar aspect of the feet are not just reserved for firewalkers.1 They can occur on the folks sunbathing at the Jersey Shore. There even have been several case reports documenting sunburn on the plantar aspect of the foot of paraplegic patients who were sunbathing and not able to feel the intensity of the sun’s rays.2,3 Consider the damage done to the dorsum of the feet and the lower legs in outdoor sports like beach volleyball and aquatic sports like surfing.4
The reality is exposure to the sun without protection places our legs and feet not just at risk of developing erythema (sunburn) but continual exposure to ultraviolet radiation (UVR) will eventually cause mutation of the DNA leading to pyrimidine dimers. The combination of UV-A and UV-B exposure along with other risk factors such as genetics may lead to both melanoma and non-melanoma skin cancer.
Key Pointers And Recommendations To Pass On To Patients
What can you recommend to your patients regarding sunscreen use? The prevailing talk in dermatology lately is using a sun filtering compound that protects oneself not only from UV-B but also from UV-A exposure.
Now UV-A is mainly associated with aging while UV-B is associated with burning. However, UV-A is really the culprit when it comes to long-term damage.5 The UV-A rays hit us all year round and through glass such as the driver’s side window. These rays penetrate deeper and have been known to cause skin cancer by suppressing the immune system.5
That said, there are two commercially available compounds that are found in sunscreens that will cover both UV-A and UV-B. These compunds are Mexoryl™ SX (L’Oreal) and Helioplex® (Neutrogena). My personal favorite products that include these compounds are Anthelios SX Daily Moisturizer (LaRoche-Posay) with Mexoryl™ SX and Neutrogena® Ultimate Sport™ Sunblock Spray with Helioplex®, SPF 100 (Neutrogena).
I know, you are thinking, “SPF of 100? Really?” Well, keep in mind that SPF is a lab measurement that simply means the amount of UV exposure you need to develop sunburn while wearing a sunscreen in comparison to developing sunburn with no sunscreen use at all. An SPF of 70 means you need to be exposed to 70 times the amount of solar energy to develop sunburn than without using a sunscreen of SPF 70.
The SPF measurement is user dependent and the development of sunburn can vary by time of day when the intensity of the sun’s rays change, global location, outdoor activities and skin type of the user. Even with those high SPFs, the wearer must re-apply liberally when exposed to water, friction, rubbing, etc. In fact, the current recommendations state that one should apply sunscreen 15 to 30 minutes before exposure to sun and then again within two hours of exposure to sun to be effective.6
Overall, my hope is this summer finds you enjoying the outdoors and with no Teva® or Croc™ induced tan lines (or circles).
1. Sayampanathan SR, Ngim RC, Foo CL. Fire walking in Singapore: a profile of the burn patient. J R Coll Surg Edinb. 1997 Apr;42(2):131-4.
2. Coban YK, Uzel M, Balik O. Plantar burns after sunbathing and walking of a patient with complete spinal cord injury. Burns 2005 May;31(3):398-9
3. Chung BS, El-Toraei I, Furnas DW. Thermal injury on the foot and ankle of a paraplegic: report of a case from exposure to sunshine. J Dermatol Surg Oncol. 1978 Jun;4(6):468-9.
4. Moehrle M. Outdoor sports and skin cancer. Clin Dermatol 2008; 26(1):12–15.
5. http://www.anthelios.com/anthelios-uvraydamage.html 
6. Diffey BL. When should sunscreen be reapplied? J Am Acad Dermatol 2001; 45(6):882-885.