Does the SPF number measure when to reapply sunscreen?
Here’s the thing…
When it comes to knowing when to reapply sunscreen, the SPF number is misleading.
You can incorrectly assume that the higher the SPF number, the less frequently you can reapply.
The SPF number indicates how much protection the sunscreen offers. It tells us how much of the sun’s UVB rays it blocks and stops from affecting our skin.
It does not tell us when sunscreen should be reapplied.
How often we should reapply sunscreen is always the same – irrespective of its SPF number – at least every two hours.
If you are out in the sun on a hot day, reapply every 1 to 1.5 hours.
So, what the heck does the SPF number measure, then?
SPF number is a measure of how much UVB radiation the sunscreen blocks.
Here is how much each of these SPF blocks:
| SPF number | What it measures |
|---|---|
| 15 | blocks nearly 93% of UVB rays from affecting the skin |
| 30 | blocks nearly 97% of UVB rays from affecting the skin |
| 50 | blocks nearly 98% of UVB rays from affecting the skin |
| 100 | blocks nearly 99% of UVB rays from affecting the skin |
Is SPF 50 better than SPF 30 and 15?
SPF 50 is way better than SPF 30 and SPF 15.
To understand why it is way better, let us rewrite the above table…Pay particular attention to column 3 in the table below
| SPF number | What it measures | What does it actually mean |
|---|---|---|
| 15 | blocks nearly 93% of UVB rays from affecting the skin | 7% of the sun’s UVB radiation reaches the skin and affects our skin. |
| 30 | blocks nearly 97% of UVB rays from affecting the skin | 3% of the sun’s UVB radiation reaches the skin and affects our skin. |
| 50 | blocks nearly 98% of UVB rays from affecting the skin | 2% of the sun’s UVB radiation reaches the skin and affects our skin. |
| 100 | blocks nearly 99% of UVB rays from affecting the skin | 1% of the sun’s UVB radiation reaches the skin and affects our skin. |
Now that we understand with the two tables above how much of the sun’s UVB radiation each SPF number allows to affect our skin, let us compare and see how much each one is better or worse than the other…
| SPF number | What it does |
|---|---|
| 15 | 7% of the sun’s UVB radiation reaches the skin and affects our skin. SPF 15 offers close to 150% less protection than SPF 30 SPF 15 offers close to 200% less protection than SPF 50 |
| 30 | 3% of the sun’s UVB radiation reaches the skin and affects our skin. SPF 30 offers 50% less protection than SPF 50 (lets in 3% Versus lets in 2%) |
| 50 | 2% of the sun’s UVB radiation reaches the skin and affects our skin. |
Is SPF 100 better than SPF 50?
Yes, it is.
However, SPF 100 can irritate the skin for many people.
That’s why you don’t see SPF 100 in the shops often.
Which UV radiation does SPF protect?
SPF protects us only from UVB radiation.
Sun’s UVB radiation can cause cancer, age our skin and burn the skin. The sunburn we experience is because of UVB radiation.
Another radiation, UVA, also reaches our skin. SPF does not protect our skin from UVA radiation.
UVA radiation ages our skin and can also cause skin cancer.
Always buy only broad-spectrum sunscreens. Broad-spectrum sunscreens protect our skin from both UVA and UVB.