Summer has arrived, with daytime temperatures expected to exceed 30C across large parts of central and southern England on Friday.

The UK Health Security Agency (UKHSA) has issued a level 3 heat-health alert for London as well as east and south-east England in response, meaning action is needed to protect older people, those with chronic health conditions, young children and babies.

Health teams in the Midlands and south-west England have also been placed on level 2 alert, meaning there is an 80% chance temperatures could exceed 30C.

So what are the best strategies to stay cool when temperatures climb?

Wear loose, long-sleeved clothing

Direct sunlight heats the blood vessels in your skin, sending heat inwards towards your core and raising your body temperature. Babies are particularly vulnerable because they have a high surface area of skin relative to their volume. Wearing loose, long-sleeved clothing can help avoid this. It also guards against sunburn (see below).

Cool hands, face and feet

So-called glabrous skin, found on the palms of the hands, soles of the feet and upper parts of the face, contains a network of blood vessels devoted to rapid temperature management. Applying cold water or an ice pack to these areas hastens body cooling. Wetting the skin, with a cold flannel for example, also helps to remove body heat through evaporation, which is the same reason we sweat.

Avoid cold showers

Counterintuitive as it may seem, a cold shower may help to conserve body heat by causing blood vessels in the skin to constrict. This undermines one of the body’s key strategies for heat loss: bringing blood closer to the skin’s surface, so the heat can radiate out (hence why we look flushed when we are hot). Longer immersion in cold water, such as going for a swim in a lake, will gradually cool the body – but cold showers tend to be swift affairs. Showering in tepid water is better because this will boost blood flow to the skin, increasing heat loss.

Stay hydrated

A significant reason heatwaves are so deadly is dehydration. When people lose too much fluid through sweating, the blood thickens, increasing the risk of clots and forcing the heart to work harder. Heavy sweating also alters the balance of sodium and potassium in body fluids. This can affect nerve and muscle cells, placing further strain on the heart. They key thing is to drink regularly through the day, avoiding caffeine and alcohol, which can cause you to urinate more frequently. Do not rely on thirst, which can be an unreliable indicator of hydration status.

Keep curtains and windows closed during the day

This is particularly important for south-facing rooms, where having the sun streaming through your windows will transform your surroundings into a greenhouse. As a general rule, windows should be kept closed when it is cooler indoors than out, usually when the day is at its hottest, but opened once the daytime temperature drops in the evening and overnight.

Seek green spaces

Trees and plants absorb water through their roots and emit it through their leaves through a process called transpiration. This cools their immediate surroundings, as heat from the surrounding air causes this water to evaporate. Studies suggest suburban areas with mature trees are 2-3C cooler than suburbs without trees. Trees also provide much-needed shade.

Avoid sunburn

No one wants blistered, swollen skin but sunscreen should be your last line of defence against the sun, rather than your first. Instead, make use of shade when the UV index is at its highest – generally between 11am and 3pm – cover skin with clothing, and protect your head, neck, and face with sunglasses and a wide-brimmed hat. If sun exposure is unavoidable, opt for a sunscreen with broad protection against UVA and UVB rays. The sun protection factor (SPF) refers to UVB protection only.

“We recommend a sunscreen with a minimum SPF of 30 and good UVA protection,” said Dr Tanya Bleiker, the president of the British Association of Dermatologists. “Sunscreen should be applied liberally, and reapplied every two hours, after swimming, exercise, or any other activity which could rub or wash it off.”