Brits miss ten percent of their face on average when applying sunscreen - the most common site for skin cancer, according to new research.
Most are still at risk of the disease - despite reaching for the factor 30 during the current summer heatwave.
Areas around the eyes and nose are especially vulnerable, warn scientists.
More than 90 per cent of basal cell carcinomas, the most common cancer in the UK, occur on the head or neck.
Meanwhile, between five and 10 per cent of all skin cancers are found on the eyelids, specifically.
Dr Kevin Hamill, of the University of Liverpool, said: "It is 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."
His team got 57 men and women to apply sunscreen to their face without supplying them with any further information or instructions.
Photos were taken of each of the participants with a camera sensitive to UV (ultraviolet) before and afterwards, which made the covered areas appear black.
A custom designed program then segmented and analysed the images to judge how successful each person was at covering their whole face.
It found they missed an alarming 9.5 per cent, on average, the British Association of Dermatologists annual conference in Liverpool was told.
The most common place was the area between the inner corner of the eye and the bridge of the nose, known as the medial canthal region (77%), and the the eyelids (13.5%).
However, when the researchers asked the participants back to repeat the experiment they did slightly better when provided with extra information about skin cancers of the eyelid.
This time an average 7.7 percent of the face was left unprotected, suggesting a public health campaign is required.
As applying sunscreen here is not necessarily practical in light of manufacturers' warnings to keep products out of the eye, Dr Hamill said it is important to use other forms of protection such as sunglasses.
He said: "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 onboard.
"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."
The findings follow a study by the the British Association of Dermatologists in May that found eight out of 10 Brits don't even apply sunscreen before going out in the sun.
Skin cancer rates in the UK have been climbing since the 1960s. Every year over 250,000 new cases of non-melanoma skin cancer - the most common type - are diagnosed.
This is in addition to over 13,000 new cases of melanoma, the deadliest form that results in around 2,148 deaths annually.
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 (European Conformity) mark and British Standard (BSEN1836), and to spend time in the shade when the sun is at its hottest between 11am and 3pm."