SPF Simplified: Making Sense of Sunscreen


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Sun Protection Factor, commonly known as SPF, is a measure of how well a sunscreen will protect skin from harmful ultraviolet rays. It indicates the level of protection against sunburns caused by UVB radiation.

Understanding SPF Ratings

SPF ratings typically range from 15 to 50+, with higher numbers indicating greater protection.

However, it’s crucial to understand that SPF does not linearly correlate with protection. SPF 30 does not offer double the protection of SPF 15; rather, it blocks about 97% of UVB rays compared to SPF 15’s 93%.

Sunscreen extends the time it takes for UVB rays to cause sunburn on your skin. For instance, if your skin would normally burn after 10 minutes in the sun, applying SPF 30 sunscreen theoretically allows you to stay in the sun for 30 times longer without burning, provided you apply it correctly.

Choosing the Right Sunscreen

The appropriate SPF level varies depending on factors such as skin type, time of day, and geographic location. Individuals with fair skin or those in regions with intense sunlight may benefit from higher SPF levels.

No matter the SPF rating, sunscreen should be reapplied every two hours, or more frequently if swimming or sweating heavily. This ensures continuous protection against UVB rays.


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Additional UV Protection

  • Sunglasses: When shopping for sunglasses, prioritize pairs that offer 100% UV protection. This ensures that both UVA and UVB rays are blocked, reducing the risk of eye damage, cataracts, and other vision problems caused by sun exposure.
  • Clothing: Wearing clothing with built-in UV protection adds an extra layer of defense against harmful rays. Look for garments labeled with UPF (Ultraviolet Protection Factor) ratings, which indicate how effectively the fabric blocks UV radiation. Darker, tightly woven fabrics generally offer better protection than lighter, more loosely woven ones.
  • Hats: Hats are another valuable tool for shielding your face, neck, and scalp from UV damage. Opt for wide-brimmed hats that shade your face and neck, providing coverage to areas often overlooked by sunscreen. Materials like tightly woven straw, fabric, or canvas offer better protection than loosely knit options.


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Consistent use of sunscreen with adequate SPF can help prevent sunburns, premature aging, and skin cancer caused by UV exposure. By also incorporating sunglasses, UV-protective clothing, and hats into your sun safety routine, you can minimize your exposure to harmful UV rays. Remember that UV rays are present year-round, so practicing sun safety habits should be a priority regardless of the season.

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Ivan Yong

Dr. Ivan Yong is an optometrist with over 12 years of experience in the optical industry. He earned his doctorate from the Southern California College of Optometry and has practiced in multiple settings, including private practice, community health, and ophthalmology. Dr. Yong aims to expand access to affordable eyewear and improve eye health worldwide.