Experts have urged people to wear sunglasses or apply sun cream around their eyes properly to protect against skin cancer.
University of Liverpool researchers said people miss on average 10% of their face when applying sunscreen.
The face is the most common site for skin cancer - more than 90% of basal cell carcinomas, the most common cancer in the UK, occur on the head or neck. Between five and 10% of all skin cancers occur on the eyelids specifically.
Researchers asked 57 participants to apply sunscreen to their face with no further information or instructions given. Photos were then taken of each participant with a UV-sensitive camera before and after the application of sunscreen, with areas covered with sunscreen appearing black due to the UV camera.
These images were then segmented and analysed by a custom-designed program to judge how successful each person was at covering their whole face.
On average, people missed 9.5% of the whole face, with the most commonly missed areas being the eyelids (13.5%) and the area between the inner corner of the eye and the bridge of the nose (77%).
The researchers then asked the participants back to repeat the experiment, this time giving extra information about skin cancers of the eyelid region.
Armed with this information there was a slight improvement in the level of sunscreen coverage with 7.7% of the face left unprotected.
As applying sunscreen in these areas is not necessarily practical due to manufacturers’ warnings to keep products out of the eye, it is important to use other forms of protection such as sunglasses, they said.
Dr Kevin Hamill, from the University’s Department of Eye and Vision Science, said: “It’s worrying that people find it so hard to sufficiently apply sunscreen to their face, an area which is particularly at risk of skin cancer due to the amount of sun exposure it receives.
“Our research shows that simple health messaging can help improve this problem, and we hope that industry groups and public health campaigners can take this on board.”
He added: “Perhaps the most important thing to take away from this research is the importance of sunglasses. Most people consider the point of sunglasses is to protect the eyes, specifically corneas, from UV damage, and to make it easier to see in bright sunlight. However, they do more than that, they protect the highly cancer prone eyelid skin as well.”
Matthew Gass, of the British Association of Dermatologists, said: “As sunscreen is one of the main protections against UV damage and skin cancer it is vital that people understand how to apply it.
“Skin cancer is the most common type of cancer in the UK, and numbers continue to rise at a worryingly fast rate.
“We still want people to enjoy themselves outdoors, but to go back to the basics of sun protection, especially those with fair skin that burns easily, and during periods of strong sunshine either in the UK or abroad.
“These are to thoroughly apply and reapply sunscreen with a minimum of factor 30 and good UVA protection, to wear protective clothing such as a t-shirt or a hat, to wear sunglasses that show the CE mark and British Standard (BSEN1836), and to spend time in the shade when the sun is at its hottest between 11am and 3pm.”