What does the SPF rating really mean?

What does the SPF rating really mean?


When it comes to sun protection, we often hear about the importance of SPF. Whether it's on sunscreen bottles, skin care products, or beauty advertisements, SPF is touted as a crucial factor in safeguarding our skin from the harmful effects of the sun. But what does the SPF rating in sunscreen really mean? In this blog, we will delve into the science behind SPF, its significance in protecting our skin, and how to make the most of this important sun protection metric.

Understanding SPF

SPF stands for Sun Protection Factor. It is a numerical rating system used to measure a product's ability to block UVB (ultraviolet B) radiation, which is the primary cause of sunburn. The SPF number indicates how long it takes for the skin to redden or burn when exposed to sunlight compared to when no sunscreen is applied. For instance, if you’re exposed or unprotected skin begins to burn after 10 minutes of sun exposure, applying sunscreen of SPF 30 would extend that time to 300 minutes or 5 hours.

The SPF rating is not directly proportional to the level of protection offered. Instead, it represents a rough estimation of the level of UVB protection.

What does the SPF rating really mean?

SPF 15: Provides 93% UVB protection
SPF 30: Provides 97% UVB protection
SPF 50: Provides 98% UVB protection
SPF 100: Provides 99% UVB protection

It's important to note that no sunscreen can offer 100% protection. Additionally, SPF does not measure protection against UVA (ultraviolet A) rays, which can cause long-term skin damage and ageing.

Factors Affecting SPF Efficacy

What does the SPF rating really mean?

While SPF plays a crucial role in sun protection, it's important to understand that its effectiveness is influenced by several factors:

  • Application Amount: To achieve the stated SPF level, an adequate amount of sunscreen must be applied. Experts recommend using about one ounce (a shot glass full) for full- body coverage. The insufficient application reduces the SPF's effectiveness.
  • Reapplication: Sunscreen should be reapplied at regular intervals, especially after swimming, sweating, or towelling off. Even the highest SPF-rated sunscreen loses its efficacy over time, so regular reapplication is essential for continuous protection.
  • Sunscreen Type: Different sunscreen formulations offer varying degrees of protection. Broad-spectrum sunscreens provide protection against both UVA and UVB rays, whereas sunscreens labelled as "water-resistant" or "sport" are designed to withstand water and sweat better.
  • Skin Type: People with fair skin are generally more susceptible to sunburn and require a higher SPF to achieve the same level of protection as those with darker skin. However, everyone, regardless of skin type, should prioritise sun protection.

Importance of Sun Protection

Sun protection is essential for safeguarding our skin health and preventing the damaging effects of UV radiation. Prolonged exposure to the sun without proper protection can lead to sunburn, premature skin ageing, wrinkles, sunspots, and an increased risk of skin cancer.

Using a broad-spectrum sunscreen with a minimum SPF of 30 is recommended by dermatologists to protect against both UVA and UVB rays. Additionally, seeking shade during peak sun hours (10 a.m. to 4 p.m.), wearing protective clothing, and using sunglasses are vital sun protection practices.


Understanding the SPF rating is crucial for making informed decisions about sun protection. While SPF provides an estimation of a product's ability to block UVB rays, it's important to remember that it does not account for UVA protection or the need for proper application and reapplication.

To protect our skin effectively, we must choose a broad-spectrum sunscreen with an appropriate SPF, apply it generously, and reapply as directed. Complementing sunscreen use with other sun protection measures, such as seeking shade and wearing protective clothing, will further enhance our defence against harmful UV radiation.

Remember, sun protection is not just a summertime concern. It should be practised year-round, regardless of the weather conditions, to ensure optimal skin health and reduce the risk of long-term damage. So, the next time you reach for sunscreen, remember to look for a high SPF, apply it generously, and enjoy the sun responsibly while keeping your skin safe.

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