Ask An Expert: Dr. Michael Carletti, UNT HSC

Thursday, July 8, 2021

Michael Carletti, UNTHSC

UNT System HR brings you UNT World experts with this periodic and always timely installation called "Ask An Expert." So, let's ask...

EXPERT: Dr. Michael Carletti, Assistant Professor of Dermatology at UNT HSC and Assistant Program Director of the Medical City Weatherford Dermatology Residency Program, practices medical, surgical and cosmetic dermatology ranging from diagnosing and treating skin cancers to performing neuromodulator injections such as Botox, Dysport, and Xeomin.

The Texas summer sun is intense, can be extreme and is always a danger to cause skin damage, multiple types of skin cancer, eye damage and even immune system suppression. Fortunately, we have experts at UNT World and HSC's Dr. Michael Carletti is here to make sense of sunscreens, SPFs, UVAs, UVBs and how best to protect ourselves and our families from the sun's harsh rays. Read on for everything you need to know.

Let’s start with the basics: What is it about the sun’s rays that can be harmful to our skin, and what are some of the risks we run from too much unprotected exposure to the sun?
Everybody needs some sun exposure to produce vitamin D (which helps calcium absorption for stronger and healthier bones). But unprotected exposure to the sun's ultraviolet (UV) rays can cause damage to the skin. This damage can lead to skin cancer or premature skin aging (photoaging). UVA and UVB ultraviolet rays reach the earth's surface. UVB rays cause a much greater risk of skin cancer than UVA. UVA rays cause aging, wrinkling and loss of elasticity of the skin. UVA also increases the damaging effects of UVB, including skin cancer and cataracts.

We know using sunscreen can help prevent skin damage, but there’s so many products, such a wide range of SPF levels, protection against UVA and UVB, that it can be confusing what to buy. Can you simplify this for us?
Sunscreens protect the skin against sunburns and play an important role in blocking the penetration of ultraviolet (UV) radiation. But no sunscreen product blocks UV radiation 100%. The protection provided by a sunscreen is indicated by the sun protection factor (SPF) listed on the product label. Sunscreens (chemical blockers) contain ingredients that help absorb UV light. Sun-blocks (physical blockers) contain ingredients such as zinc oxide and titanium dioxide that physically scatter and reflect UV light. Choose a broad-spectrum sunscreen that filters out both ultraviolet A (UVA) and ultraviolet B (UVB) rays. To protect your skin from the sun’s harmful rays, you want to use a sunscreen that offers all of the following:

  • SPF 30 (or higher)
  • Broad-spectrum protection (UVA/UVB)
  • Water resistance

Chemical Sunscreen

  • Less is needed to protect the skin because there is no risk of spaces between the sunscreen molecules after application
  • Tends to be thinner and spreads more easily on the skin


  • Requires about 20 minutes after application before it starts to work
  • Increased chance of irritation and stinging due to the multiple ingredients combined in order to achieve broad spectrum UVA and UVB protection
  • The higher the SPF, the higher the risk of irritation for sensitive skin types
  • The protection it offers gets used up more quickly when in direct UV light, so reapplication must be more frequent.
  • May clog pores for oily skin types

Physical Sunscreen


  • Offers protection against both UVA and UVB rays and is naturally broad-spectrum
  • Protects from the sun as soon as it’s applied, no wait needed
  • Lasts longer when in direct UV light, but not when wet or sweating
  • Less likely to cause a stinging irritation on the skin
  • Less likely to be pore-clogging, making it ideal for acne-prone skin
  • Longer shelf life


  • Can rub off, sweat off and rinse off easily, meaning more frequent reapplication when outdoors as needed
  • May leave a white film on the skin, making some formulas incompatible for medium to dark skin tones
  • Can be less protective if not applied and re-applied generously and accurately since UV light can get between the sunscreen molecules and get into the skin

Regardless of which sunscreen you choose, it is important to make it part of your daily skin care routine. Regular application of sunscreen can reduce your chances of skin cancer while also prolonging the development of wrinkles and sun spots.

OK, so when spending the day at the pool, lake or beach, sunscreen is absolutely necessary. But what about short stints outdoors such as a morning dog walk or mowing the lawn, is it really necessary to apply sunscreen then?
The answer is yes, ALWAYS. 

  • Limit time in the midday sun -- the sun's rays are strongest between 10 a.m. and 4 p.m. Limit exposure to the sun during these hours, even in winter and especially at higher altitudes
  • Wear protective clothing such as a long-sleeved shirt, pants, a wide-brimmed hat, and sunglasses, whenever possible. Look for clothing with a UV protection factor (UPF)
  • Watch the UV Index. The UV Index provides important sun safety information to help people plan outdoor activities
  • You can even get a sunburn on cloudy or cooler days along with on long car road trips as most windows and tints do not protect from all UV rays

What are some warning signs of skin damage, when should we see a doctor and should we visit a general physician, a dermatologist or another type of doctor? 
Regardless of your exposure to UV rays, conduct a monthly self-check to look for any skin abnormalities. Have a friend or family member check your back and scalp. Look for bumps or sores that don't heal or bleed and also for moles that have changed size, color or shape. It’s important to visit your physician or a dermatologist for regular skin checks. When caught early, most cases of skin cancer can be easily cured.

Are people with darker complexions less susceptible to sun damage?
Many people believe that dark skin is not susceptible to sun damage. However, although dark skin tones are less likely to burn, people of almost every skin tone can get sunburnt or develop skin cancer. Darker skin has more protection from the sun because it contains higher levels of melanin. This is the pigment that gives the skin its color and helps protect the cells from some forms of sun damage. This makes people with darker skin less likely to experience sunburn, but it is still possible.

How about children, is their skin extra sensitive to the sun’s rays? Can children use the same sunscreen as their parents or do they need sunscreen for children?
It is recommended to not use sunscreen on infants less than 6 months old. Any child 6 months or older can use the same sunscreen as adults. Keep your baby in the shade. Shade is the best way to shield your baby from the sun, especially if he or she is younger than 6 months old. Keep your baby in the shade as much as possible, and if you can’t find shade, create your own using an umbrella, canopy or the hood of a stroller. Dress your baby in sun-protective clothing, such as a lightweight, long-sleeved shirt and pants. In addition, make sure your baby always wears a wide-brimmed hat and sunglasses with UV protection. Minimize sunscreen use on children younger than 6 months old. However, if shade and adequate clothing are not available, parents and caretakers may apply a minimal amount of broad-spectrum, water-resistant sunscreen with an SPF of at least 30 to their children’s skin. It is recommended to use sunscreens containing titanium dioxide or zinc oxide as they are less likely to irritate a baby’s sensitive skin. Remember to reapply your child’s sunscreen every two hours or immediately after swimming or sweating, as there is no such thing as “waterproof” sunscreen.

When it comes to sunscreens, is there any difference in effectiveness in sprays, creams or a block (like a stick of deodorant)?

  • Any sunscreen use is better than no sunscreen use. Keep in mind, one ounce of sunscreen (enough to fill a shot glass) is considered the amount needed to cover the exposed areas of the body
  • Spray sunscreen studies show that many people apply only one-quarter the needed amount. In order to achieve a sun protection factor (SPF) similar to a lotion, you need to spray each body area for up to six seconds
  • The best way to protect yourself against the damaging effects of the sun is to limit exposure and protect your skin
  • Apply sunscreen on all exposed skin 20 minutes before going outside/exposure
  • Generously apply a broad-spectrum water-resistant sunscreen with an SPF (Sun Protection Factor) of at least 30 to all exposed skin. Broad spectrum means the sunscreen protects you from both UVA and UVB rays
  • Reapply about every 2 hours and after swimming or sweating
  • Don’t forget to protect your lips and ears

Any additional information we should know?
Skin cancer is the most common cancer in the U.S., but it is also one of the most preventable cancers. One in five Americans will develop skin cancer in their lifetime.