Sunburn timeline: Exactly how your body fights - and loses to suburn in minutes and years

Wearing sunscreen should be as routine as brushing teeth or wearing a seatbelt or a bike helmet.

Yet many of us – particularly those intent on getting a tan – will have felt that hot, tingling sensation on our shoulders already this month and kicked ourselves for not protecting our skin.

The Telegraph reports that around half the British population get sunburnt at least once a year, according to a study by Melanoma Focus. Younger people are the most careless, with 65 per cent of 18 to 32 year olds getting burnt. The same study also revealed that 36 per cent of British people rarely or never apply sunscreen when in the UK during summer months – a figure that increases to 42 per cent for men.

You might not feel it yet, but the damage has already started. Within just 15 minutes of unprotected sun exposure, UV radiation is penetrating the outermost layers of your skin and starting to cause harm. “UVB radiation starts damaging DNA,” Dr Sommerlad says.

“The body’s immune system recognises this damage and triggers an inflammatory response. Blood vessels dilate, which is why in those with lightly pigmented skin, the skin can look red and feels warm and tender. This response is your body trying to bring immune cells to the area to repair the damage. In those with deeply pigmented skin, redness may be less perceptible but instead the skin may feel warm and tender.”

The warmth, tenderness and swelling can ramp up as the immune response gathers pace, according to Dr Sommerlad. “Blistering may appear in very extreme cases – a troubling sign of dead skin cells that have lost the ability to remain cohesive.”

Pain worsens as inflammation from UV damage activates nerve cells. In very severe cases there may be flu-like symptoms such as chills, aching and nausea, triggered by inflammatory chemicals entering the bloodstream after extensive UV exposure.

Peeling kicks in as the body sheds damaged skin cells, an attempt to get rid of cells with DNA too badly hit to repair. “The skin may remain red or darker than the original skin colour. Itchy skin occurs as wound healing events start to occur in the sun burnt areas,” Dr Sommerlad says. The process of healing the skin can release chemicals in the skin that increase the sensation of itch, she says, a bit like when you have an itchy scab.

As the acute pain and swelling fade, patchy pigmentation can start to show. It’s the result of excess eumelanin produced after UV exposure, and it often shows up as freckles and sun spots known as solar lentigos. “These are often permanent but may fade in less sunny months only to reappear in sunnier weather. Others do not fade even in the winter months,” Dr Sommerlad explains.

“It is important to regularly monitor your skin for any changes, particularly moles,” agrees Clare O’Connor, a suncare scientific advisor at Boots. “If you do notice anything unusual, you should visit your GP, an NHS Walk-in Centre or a pharmacist.”

A mole scanning service is available in selected Boots stores, while a SmartSkin Checker, an AI-powered skin tool that can screen for over 70 skin conditions, is available via Boots Online Doctor.

Your skin doesn’t forget a burn. Even when the tan has gone, long-term effects can linger. Hyperpigmentation may appear as patchy pigment, freckling and sun spots, sometimes called liver spots or age spots, Dr Sommerlad says. “Fine lines and loss of firmness can also be observed.”

These changes are broadly described as photo damage and they give skin a prematurely aged look. UV exposure can also affect the eyes, with damage linked to early cataract formation and growths on the surface of the eye, such as pterygium, which can impair vision. The World Health Organization (WHO) estimates that up to 20 per cent of cataracts globally are the result of UV overexposure.

Over time, repeated sunburns add up. Cumulative DNA damage can overwhelm the skin’s repair systems, causing mutations in the genes that control cell growth and potentially leading to pre-cancerous and cancerous changes, Dr Sommerlad says.

We know melanomas arise through a complex interplay involving melanocytes — the pigment-producing cells — going into uncontrolled growth and division. “It is difficult to pinpoint exactly when and why melanomas form,” she says. “We do know that some people are much more likely to get them.”

Up to 86 per cent of melanomas are preventable if you protect your skin in the sun, according to Melanoma Focus, using sunscreen and protective clothing. SPF stands for sun protection factor and measures the product’s protection against UVB rays; if your skin would burn in 10 minutes and SPF 30 should protect you for 30 times longer, ie about 300 minutes.