Austin Sunscreen: Is Truck Heat Ruining Protection?

By Franklin Everett Shaw

October 31, 2025

The midday sun beats down on Congress Avenue, turning car interiors into ovens. You reach for your trusty sunscreen, the one you stashed in the glove compartment for emergencies. But is it still protecting you? In Austin’s relentless heat, especially inside a parked car, your sunscreen might be doing more harm than good.

Sunscreen degradation in high temperatures is a serious concern, particularly in places like Austin, Texas, where summer temperatures routinely soar. The active ingredients in sunscreen, responsible for blocking harmful UV rays, can break down when exposed to excessive heat. This breakdown reduces the Sun Protection Factor (SPF), rendering the sunscreen less effective, or even completely useless.

Let’s consider two popular sunscreen brands readily available in Austin: EltaMD and La Roche-Posay. EltaMD sunscreens, often recommended by dermatologists, frequently contain zinc oxide and titanium dioxide as active ingredients. While these mineral sunscreens are generally more stable than chemical sunscreens, they are still susceptible to degradation at extremely high temperatures. La Roche-Posay, known for its broad-spectrum protection, often utilizes a combination of chemical filters. These chemical filters are particularly vulnerable to heat-induced degradation.

The interior of a car parked in the Austin sun can easily reach temperatures of 150-190°F (65-88°C). Studies have shown that prolonged exposure to temperatures above 104°F (40°C) can significantly reduce the SPF of many sunscreens. This means that the EltaMD or La Roche-Posay sunscreen you diligently applied might be offering significantly less protection than the label indicates after just a few hours in your car.

So, what can Austin residents do to ensure their sunscreen remains effective? Proper storage is key.

• Avoid Storing Sunscreen in Your Car: This is the most crucial step. The glove compartment or center console are not suitable storage locations.
• Store Sunscreen in a Cool, Dark Place: Keep your sunscreen indoors, away from direct sunlight and heat sources. A bathroom cabinet or a drawer in your bedroom are better options.
• Use a Cooler Bag: If you’re heading to Zilker Park or Barton Springs Pool, pack your sunscreen in a cooler bag with an ice pack to maintain a lower temperature.
• Check the Expiration Date: Sunscreens have an expiration date, and using expired sunscreen is never a good idea. The active ingredients degrade over time, regardless of storage conditions.
• Consider Smaller Tubes: Opt for smaller tubes of sunscreen that you can easily carry with you and use up quickly. This minimizes the amount of sunscreen that sits around potentially degrading.

Want to see the degradation for yourself? Here’s a simple DIY experiment you can conduct:

1. Gather Your Supplies: You’ll need two identical tubes of sunscreen (EltaMD or La Roche-Posay work well), two clear glass plates, a UV flashlight (available online), and a UV detection card (also available online).
2. Control Sample: Store one tube of sunscreen in a cool, dark place indoors. This will be your control sample.
3. Heat Exposure: Place the other tube of sunscreen in your car on a hot day (aim for a day above 95°F). Leave it there for at least 4 hours.
4. Application: Apply a thin, even layer of both the control sunscreen and the heat-exposed sunscreen onto separate glass plates.
5. UV Light Test: In a darkened room, shine the UV flashlight onto both glass plates. Place the UV detection card behind each plate.
6. Observe the Results: The UV detection card behind the control sunscreen should show significantly less UV light penetration compared to the card behind the heat-exposed sunscreen. This demonstrates the degradation of the sunscreen’s protective capabilities due to heat exposure.

This experiment, while not scientifically rigorous, provides a visual representation of how heat can compromise sunscreen effectiveness.

Beyond proper storage, consider these alternative sun protection strategies, especially when driving or spending extended periods outdoors in Austin:

• Window Tinting: Invest in window tinting for your car. This can significantly reduce the amount of UV radiation entering the vehicle.
• Sun-Protective Clothing: Wear long sleeves, pants, and a wide-brimmed hat when possible. Many brands offer clothing with UPF (Ultraviolet Protection Factor) ratings.
• Sunglasses: Protect your eyes with sunglasses that block 100% of UVA and UVB rays.
• Seek Shade: During peak sun hours (10 AM to 4 PM), seek shade whenever possible. This is especially important when participating in outdoor activities like hiking the Greenbelt or kayaking on Lady Bird Lake.
• Reapply Frequently: Sunscreen should be reapplied every two hours, or more often if you’re sweating or swimming. Don’t rely on a single application in the morning.

One common mistake people make is assuming that a higher SPF provides significantly more protection. While SPF 30 blocks about 97% of UVB rays, SPF 50 blocks about 98%. The difference is minimal, and proper application and frequent reapplication are far more important than chasing the highest SPF number.

Another pitfall is neglecting to apply sunscreen to often-overlooked areas like the ears, neck, and tops of the feet. These areas are particularly vulnerable to sun damage.

Living in Austin means embracing the outdoors, but it also means taking sun protection seriously. Don’t let the Texas heat compromise your sunscreen’s effectiveness. By following these storage tips and adopting alternative sun protection strategies, you can enjoy the Austin sunshine safely and responsibly. Remember, protecting your skin is an investment in your long-term health.