Sunscreens: a front-line defence against aging and skin cancer but are the chemical-based ones safe?

Daniel Judd BSc, MBiol

Sunscreens play a vital role in our anti-aging regime and against skin cancer but some contain chemicals that are raising alarm bells. Daniel Judd investigates.

Sunscreens are a hugely important in skin care. The light from the sun contains rays of invisible, high energy ultraviolet light (UV). When it hits your skin, UV causes all sorts of problems including sunburn, wrinkles and skin cancer. These three things are all a result of UV’s ability to damage your DNA. The UV that damages our skin comes in two varieties; UVA and UVB which penetrate the skin to different depths with the UVB more responsible for superficial burning and the UVA reaching into the deeper skin layers.

While it was previously thought that UVB was the main culprit when it comes to creating cancerous changes in the skin, research is now pointing toward UVA as a major cause for non-melanoma skin cancers like basal cell carcinoma and squamous cell carcioma.  UVB targets your DNA directly, sticking bits of it together in ways that lead to skin cancer (melanoma) mutations while UVA causes indirect damage by creating reactive molecules called free radicals in your cells which attack your DNA creating breaks in it.

Mutations in your DNA are what cause cancer to form and your skin tries to prevent this by triggering the inflammation seen during sunburn which lets your immune system deal with the damaged cells. Unfortunately, this inflammation also damages collagen fibres in the affected area, leading to wrinkles and sagging of the skin. The effect is so common that UV exposure is thought to be the leading cause of premature skin aging.



Sunscreens protect from this damage by absorbing the UV rays as they hit the skin. When light gets absorbed, it’s quickly spat back out again but at a lower energy, changing absorbed UV into visible or infrared light. The two main groups of sunscreens are chemical (benzophenones, camphors, and cinnamates) and mineral (titanium dioxide and zinc oxide). Each sunscreen ingredient works best at absorbing a particular wavelength of UV, some might absorb some UVA wavelengths, while others might absorb some or almost all UVA and UVB wavelengths, so most commercial sunscreens contain a mix of several active ingredients, both chemical and mineral, to increase protection and coverage.

With such apparent benefits to sunscreen use, it’s easy to think they can do no wrong but there are growing concerns regarding the widespread, regular use of sunscreens, particularly chemical sunscreens.


Hormonal disruption 

A major cause for concern with chemical sunscreens is the possibility that once they’ve been absorbed into your body, they can have serious unintended effects, particularly on the function of your sex hormones: oestrogen and testosterone. The concern is based on the fact that many chemical sunscreens including oxybenzone, octinoxate and homosalate are similar enough in shape to these hormones that they can mimic them. Hormones need to interact with proteins to switch on signals in the body and these chemical sunscreens can sometimes bind to the same proteins, either blocking the hormone or switching on the signal itself.

There have been many tests of this effect on animals or human cell cultures. In rats and fish, benzophenones have been shown to mimic oestrogen and interfere with the reproductive cycle. Tests on human breast cancer cells showed oxybenzone was able to act as an oestrogen and switch on oestrogen signals. In many breast cancers, these oestrogen signals increase the growth and spread of cancer. While this research is pretty damning, the fact remains that these hormone mimicking and disrupting effects haven’t actually been observed in live humans. One study did look at the effect of adults regularly using camphor, benzophenone and cinnamate based sunscreen on oestrogen and testosterone levels and found that no changes in these hormones were caused by the chemicals in the sunscreen. The researchers here did also note that only adults were included in this study and that prepubescent children may be more susceptible to hormone disruption.



Biological effects can vary greatly between animals and humans as well as human cell cultures and a complete human body so while concerning, evidence of hormone disruption in animals and cell cultures can’t speak conclusively for the effects of a chemical in its real-world application.



A major drawback for some when it comes to the use of chemical sunscreens is the possibility of allergic reaction. The commonly used chemical sunscreens can all trigger contact dermatitis in some individuals. Rates of allergic reaction vary between different sunscreens and those with pre-existing sensitive skin conditions may be more likely to have a bad reaction.

The reaction of a rash, blistering or itching may not trigger immediately but instead flare up when the skin coated in the sunscreen is exposed to the sun’s UV rays, this is known as photocontact dermatitis. While this might not be a problem in other products, a sunscreen that you can’t wear in the sun isn’t the most useful of items.

It should be noted that early reporting on photoallergies to sunscreen might have overstated the number of people affected. Modern tests have found only a small fraction of the population to be affected by such allergies and believe early test results were skewed by mainly testing those with pre-existing skin conditions.


So how worried should you be?

As it stands, there’s a lot of research on animals and on cell lines to suggest the commonly used chemical sunscreens can cause major hormonal problems, but, and this is a big ‘but’ – there is little to no evidence of this being true in the real world use of these sunscreens on humans.

The chemical sunscreens may also trigger unpleasant allergies in some but it doesn’t look like they’re interfering with your vitamin D levels.

If you are concerned about any of the above, there are alternatives. Mineral only sunscreens aren’t implicated in any hormonal disruption effects and they’re usually less allergenic than chemical or mixed sunscreens. They also have good UVA and UVB coverage on their own without additional chemical sunscreens mixed in. The choice is yours.