Some people love the smell of sunscreen, because it reminds them of summer – as if the increasingly horrific heat and ubiquitous summer anthems aren’t enough.

Either way, sunscreen is a scientific marvel, something that prevents serious damage to your skin, and a new study is emphasizing that we really aren’t using enough of it. As a new paper – published in Acta Dermato-Venereologica – explains, we’re often getting less than half of the required protection, perhaps around 40 percent.

As elucidated by Live Science, sunscreen contains a mixture of inorganic and organic compounds, the former of which reflects or scatters light away from your skin, and the latter of which absorbs ultraviolet (UV) radiation, preventing the skin from doing so.

There are three categories of UV radiation: UVA, UVB, and UVC. The first has the longest wavelength, and the last has the shortest. UVC is often absorbed by the ozone layer, but the other two make it down to the surface. UVB is more energetic and more damaging dose-by-dose than UVA, but UVA makes up the vast majority of our exposure.

Able to easily penetrate through our skin, UVA causes damage to the skin, contributes to sunburn, and increases the chance of skin cancers appearing down the line. UVB rays trigger sunburn, and play a key role in the development of skin cancer.

That’s where the Sun Protection Factor (SPF) comes in. In most cases, it refers to how well the sunscreen you’re using protects you against UVB. There is currently no standard way of measuring UVA protection, but the Skin Cancer Foundation notes that you should look for the words “broad spectrum” on the label, which means the cream/spray/lotion covers a range of UV wavelengths.

So what’s with the number? Well, it’s an approximation: it tells you how long it would take UV radiation to turn your skin red if you used the product properly. So, SPF 30 means that it would take you 30 times longer to burn than if you weren’t wearing sunscreen.

This new study finds that, unsurprisingly, we aren’t using it properly.

Even if we do, we spend more time in the Sun anyway, which can effectively lead us to getting more radiation than we would expect. The problem the team from King’s College London looked at, though, was how we apply the sunscreen.

Throughout a series of experiments – on fair-skinned volunteers, but everyone is vulnerable to sunburn and skin cancer – they simulated UV exposure in various doses, equivalent to a temporary venture into sunlight, and a longer-term exposure matching that of a vacation somewhere sunny. As they did, they applied varying thicknesses of sunscreen.

As expected, the team found more DNA damage in the skin that had been left unprotected, even when the dose was very low. The thicker the sunscreen, the better protected the skin was.

Here’s the kicker: SPF ratings are based on the idea that we put a 2-milligram splodge of sunscreen on every tiny 1-square-centimeter patch of skin. Basically, a thick layer.

Turns out that we often put on far less than this in our rush to get outdoors. As the experiments show, this really ups how much genetic damage our skin experiences.

The team suggest that although many of us go for SPF 15, we should pick something far higher. In fact, even SPF 50 sunscreen applied in our typically slapdash way only gives us around 40 percent of the required protection.

The World Health Organization (WHO) notes that incidences of both types of skin cancer have been increasing in the past few decades. Don’t join this grim trend: protect your skin.