With help from Dr Zainab Laftah, consultant dermatologist and skin health educator, we explain how to pick the right sunscreen to best protect you from the sun's harsh rays.

Not just a burn

Queimadura solar can be painful and cause skin irritation, peeling and even blistering in extreme circumstances. But it can also cause more severe damage. Excessive sun exposure and sunburn can lead to câncer de pele.

Skin cancer is one of the most common cancers in the world. In the UK, more than 150,000 new cases of câncer de pele não melanoma are diagnosed each year. It affects more men than women and is more common in older people.

Around 13,500 new cases of melanoma, the deadlier type of skin cancer, are diagnosed each year.

Skin cancer can occur anywhere on the body, with most cases diagnosed in people under 50. Some 2,000 people die from melanoma each year in the UK.

If you're worried about a mole, particularly changes with any of the signs above, you should speak with your doctor as soon as possible.

The sun's UV rays are so damaging that you should be wearing sun protection even when it's cloudy.

When choosing a sunscreen you need to look for two things:

1. Does it protect against UVA and UVB rays?

2. What is the sun protection factor (SPF)?

UVA or UVB protection?

The sun emits two wavelengths of light that penetrate the earth's atmosphere - ultraviolet A and ultraviolet B.

Laftah says: "Sunscreens are rated on their level of UVA and UVB protection. I always recommend a broad-spectrum sunscreen with both UVB and UVA protection."

Because UV rays damage the skin in different ways, a sunscreen which only protects you from one type or the other isn't going to give you full protection.

"UVA rays have longer wavelengths at lower energy levels," explains Laftah. "They penetrate deeper into the skin, damaging the collagen and leading to the formation of wrinkles and skin ageing.

"UVB rays are shorter wavelengths with higher energy. They damage the DNA in the outer layer of the skin and lots of exposure increases the chance of skin cancers developing."

Every time your skin gets damaged by the sun it can cause mutations in your cells, which could lead to malignant tumours. That's why it's so important you ensure you're protected from both forms of UV rays.

A person who applies SPF15 once daily for an entire day outside is not getting enough protection. SPF15 is the lowest SPF recommended by doctors and so offers the least protection.

On top of the SPF rating, you should also look for the star rating. This reflects how well it protects against UVA rays compared to UVB.

"The SPF rating indicates the level of ultraviolet B (UVB) protection and is rated on a scale from 2 to 50+," says Laftah. "The star rating refers to the ultraviolet A (UVA) protection with a scale from 1 to 5."

Do be aware, though, that a low SPF sunscreen with a high star rating will not provide as much UVA protection as a high SPF sunscreen with the same star rating. That's because it's dependent on the ratio of UVA and UVB protection. Just another reason for picking a higher SPF product.

Laftah explains: "The SPF curve reflects the percentage of UVB blocked as the SPF rating increases - however, it is not linear and starts to plateau after 30."

She gives examples:

• An SPF of 15 indicates a protection of 93%.

• With SPF 30 this becomes 97%.

• With SPF 50 this becomes 98%.

Can people with darker skin skip SPF?

Your skin colour can play a role in your natural sun protection, but it doesn't mean you can skip sunscreen when spending time in the sun.

Use-by dates aren't just for food, they apply to sunscreen too. That's because the minerals or chemicals in the sunscreen have a life limit on how long they're likely to protect you for.

"Expired sunscreens are less likely to provide adequate protection and the likelihood of sunburn is higher," says Laftah. "They may also lead to skin irritation."

Now you know all the things you need to look for in a sunscreen, you might be interested to know about the ingredients used in the creams.

Laftah explains that sunscreens are divided into mineral and chemical creams, depending on their mode of action and the chemicals they contain.

Mineral sunscreens - for sensitive skin

According to the skin expert, the mineral (physical) sunscreens contain titanium dioxide and zinc oxide, which block the UV rays from penetrating the skin by deflecting and scattering them like tiny mirrors.

"They tend to leave a white cast which can reduce their appeal," she says. "However, they are less likely to cause irritation to your skin and may be preferred for those with sensitive skin - for example, eczema and rosacea."

Chemical sunscreens - for oily, blemish prone skin

Chemical sunscreens contain ingredients such as oxybenzone, avobenzone, octinoxate, octocrylene, octisalate, and homosalate, which are absorbed by the skin.

"They reduce UV damage by absorbing UV rays, converting them into heat before releasing this heat from the skin," Laftah explains. "They do not leave a white cast and are therefore favoured for darker skin types. They also have a lighter consistency and are preferred for oily and blemish-prone skin."