We are in the season when dermatologists most strongly emphasize the importance of sun protection. I always remind you that protecting yourself from the sun doesn’t just mean using sunscreen—it also involves avoiding peak sun hours, wearing hats and UPF clothing, and seeking proper shade.
However, creams are an excellent ally in blocking the effects of UV radiation on exposed skin that we can’t protect in other ways. For this reason, I think it’s interesting to debunk three common myths that often cause confusion when using sunscreen during holidays.
1. You need to apply sunscreen 30 minutes before sun exposure → FALSE
You’ve probably read and heard this recommendation in countless pamphlets. However, contrary to what was believed and recommended years ago, we now know that sunscreen products are effective within minutes of being applied to the skin, and no waiting time is needed for them to “activate.”
This was demonstrated by a group of researchers in Málaga a few years ago. I talk about it in this article.
From a purely practical perspective, however, this recommendation does make a lot of sense. Applying sunscreen at home, calmly and before heading to the beach or pool, likely allows for a more even and meticulous application of the product, which leads to better prevention of sun damage. It’s not the same to quickly spray sunscreen onto sweaty skin right before the first swim, as it is to thoroughly cover all dry skin with a fluid cream in a step-by-step manner.
2. The SPF number tells you how many minutes you can stay in the sun → FALSE
This is a widespread belief, but the idea that SPF 20 means you can stay in the sun for 20 minutes is completely incorrect.
SPF is the index that reflects a sunscreen’s ability to block ultraviolet B (UVB) rays, which are responsible for sunburn.
Therefore, SPF indicates how many times the minimal erythema dose (the amount of sun exposure that causes the skin to redden) is multiplied when using sunscreen compared to no protection. So, if you normally burn after 10 minutes without sunscreen, using SPF 20 would mean you could be exposed to the same intensity of sunlight for 200 minutes before burning.
However, since sunscreen can gradually be removed from the skin due to sweating, swimming, and natural skin processes, it’s always recommended to reapply it every 2–3 hours.
3. SPF 100 protects twice as much as SPF 50 → FALSE
Sunscreens available in pharmacies come in a wide range of SPF values. When looking for a good product, it’s logical to opt for SPF 100 over lower values like 50, because a higher number seems to imply better protection. It seems reasonable to think that SPF 100 protects twice as much as SPF 50.
Although this assumption is understandable and partly true, the difference in protection between the two is not double—it’s much smaller (as shown in the chart below), so small that experts consider it negligible.
