Scientific Skincare - Does Sunscreen Prevent Tanning?
Skincare

Does Sunscreen Prevent Tanning?

Wearing sunscreen every single day is categorically the best thing you can do for your skin. Up to 90% of premature skin aging is due to UV radiation which, along with some types of skin cancer, can almost entirely be avoided with adequate sun protection, but what about ‘tanning’? Does sunscreen prevent tanning?

Does Sunscreen Prevent Tanning?

The short answer is yes; sunscreen does prevent tanning but only to a certain degree. The reasons your skin may still tan while wearing sunscreen include:

  • No sunscreen blocks 100% of UV radiation – even the highest SPFs allow at least 1% of UV radiation to penetrate skin.
  • You have not applied the correct amount of sunscreen and are therefore not receiving the SPF/UVA-PF you think you are.
  • You have not reapplied your sunscreen frequently enough – sunscreen can only absorb UV radiation for a limited period of time before it needs to be reapplied.
  • Your sunscreen does not offer adequate UVA protection or the ratio of UVA to UVB protection is unbalanced – SPF50 may let you receive 50x the amount of UVB radiation before burning but PA++++ only lets you receive 16x the amount of UVA radiation before tanning.

In order to understand these reasons for why sunscreen does not always prevent tanning, we first need to understand how the radiation from the sun damages the skin, how sunscreen protects against this damage, and the difference between UVA and UVB protection.

Does Sunscreen Prevent Tanning

Ultraviolet Radiation

The radiation from the sun (solar radiation) is mostly made up of visible light, infrared (IR) radiation, and ultraviolet (UV) radiation. UV radiation is further broken down into UVA, UVB, and UVC.

UVC radiation is entirely absorbed by the earth’s atmosphere and does not pose a threat to our skin. However, both UVA and UVB cause damage, albeit in slightly different ways.

UVB has a shorter wavelength than UVA and therefore has more energy. This means that it can only penetrate the epidermis (the outer layer of the skin) but it can cause significant damage to DNA and cause the skin to burn.

UVA has a longer wavelength and therefore less energy which means that it can penetrate deeper into the skin and cause the production of free radicals which damage DNA and break down collagen and elastin.

Both UVA and UVB stimulate the production of melanin in the skin which leads to what we refer to as a ‘suntan’.

An easy way to remember this distinction is:

  • UVA = Aging
  • UVB = Burning

 

How Does UV Radiation Cause Tanning?

There are three steps involved in the increase in skin pigmentation after exposure to UV radiation (otherwise known as ‘tanning’):

  • Immediate Pigment Darkening (IPD) – a temporary darkening of pigment that occurs within minutes of UV exposure and is particularly activated by UVA radiation.
  • Persistent Pigment Darkening (PPD) – a longer phase of tanning that follows on from IPD that lasts at least 3-5 days and is more strongly activated by UVA than UVB radiation.
  • Delayed Pigment Darkening (DPD) – the last phase of tanning that is first noticeable 2-3days after sun exposure, lasts at least 3-4 weeks before beginning to fade, and can be caused by either UVA or UVB radiation.

If you are interested in the nitty-gritty details of this process, check out Part 1 of The Scientific Sunscreen Guide.

 

How Does Sunscreen Work?

There are two types of sunscreen; physical and chemical. Both physical and chemical sunscreens absorb UV rays and turn the energy to heat before that energy can be absorbed by DNA and cause damage. In addition, physical sunscreens can reflect and scatter UV rays – particularly the longer UVA rays.

A number of sunscreens contain a combination of both physical and chemical sunscreen filters which means that you don’t necessarily have to choose between the two.

However, no sunscreen can offer 100% protection against UV radiation. This means that the first reason that sunscreen does not always prevent tanning is because some amount of UV radiation is still absorbed into the skin.

The amount of protection that a sunscreen offers (%) has long been determined by the Sun Protection Factor (SPF).

 

What Is SPF?

SPF measures a sunscreen’s ability to protect the skin from UVB radiation by calculating how long it takes the skin to burn with and without sunscreen. If all other factors are equal, then this means that a sunscreen with SPF50 will allow the skin to be exposed to 50x more UVB radiation than unprotected skin before burning. However, this doesn’t take into account the fact that the strength of UVB radiation varies throughout the day and seasonally.

However, generally speaking:

  • SPF15 blocks 93.4% of UVB (6.6% still absorbed)
  • SPF30 blocks 96.7% of UVB (3.3% still absorbed)
  • SPF50 blocks 98.1% of UVB (1.9% still absorbed)

Initial research suggested that a sunscreen with SPF of 15 was enough to reduce the risk of skin cancer. However, while this is still the case, the role of UVA radiation was largely overlooked in these research studies.

 

What’s The Deal With UVA?

Due to the fact that skin damage from UVA radiation is less noticeable initially, most sunscreens didn’t offer UVA protection until fairly recently. In fact, there was a large demand for sunscreens that enhanced tanning – which basically meant that they prevented burning (usually with a very low SPF) in order for you to stay out longer in the sun and tan.

This is perhaps worse than wearing no sunscreen at all – at least sunburn alerts you to the fact that skin damage is occurring so that you can remove yourself from the sun and protect yourself from further skin damage.

Research suggests that a sunscreen with an SPF above 11 will have some protection against shorter UVA-2 wavelengths due to the fact that these wavelengths are also able to cause sunburn. In addition, broad-spectrum sunscreens are required to provide protection across the UVA spectrum but there is no requirement for how much protection is required (i.e. no UVA protection factor).

UVA protection in sunscreens is not standardized in the same way that UVB protection is. For example, in the EU, the UVA protection of a sunscreen must be at least one third that of its UVB protection – so a sunscreen with SPF30 has to offer UVA protection equivalent to at least UVA-PF10.

Another method for determining UVA protection is via the PA+ system which measures UVA protection in a similar way that SPF measures UVB protection but with a different endpoint. As mentioned earlier, Persistent Pigment Darkening (PPD) is one stage of tanning that is activated predominantly by UVA radiation. The PA+ system measures the time taken to cause a PPD response with and without sunscreen protection and the resulting value is the PPD rating.

  • PA+ = PPD between 2 and 4
  • PA++ = PPD between 4 and 8
  • PA+++ = PPD more than 8
  • PA++++ = PPD more than 16

As you can see, these values are a lot less than the most commonly used SPF values.

The ideal sunscreen should have equal UVA and UVB protection – so a sunscreen with SPF50 should, ideally, have a PPD of 50.

The closest sunscreens get to this ideal is through star rating systems, which require the UVA protection to be at least 90% of the UVB protection in order to achieve the highest 5-star ratings.

This means that the next reason that sunscreen does not always prevent tanning is due to inadequate UVA protection or an unbalanced ratio of UVA to UVB protection.

For a list of high UVA sunscreens, see here: High PPD Sunscreens.

For more information about how UVA and UVB protection is measured see here: Scientific Sunscreen Guide Part 2.

Are You Actually Getting The Stated SPF or UVAPF Protection?

Another reason that sunscreen does not always prevent tanning is because most people don’t apply the right amount of sunscreen nor reapply sunscreen as frequently as required.

Both SPF and UVA-PF values are calculated based on a specific quantity of sunscreen being applied – 2mg/cm2. That’s roughly a nickel-sized (or ten-pence-sized) dollop for the face or the equivalent of a shot glass (or two tablespoons) to cover the exposed areas of the face and body.

As mentioned earlier, sunscreen filters absorb UV radiation and transfer the energy into heat, if they are unable to transfer this energy quick enough, they cannot absorb any more UV radiation and become unstable and effectively inactive. In most cases, to prevent this from happening, sunscreen should be reapplied every 2 hours.

 

Summary – Does Sunscreen Prevent Tanning?

Sunscreen can only prevent tanning to a certain extent. The most common reasons that sunscreen does not prevent tanning include:

  • No sunscreen blocks 100% of UV radiation – even the highest SPFs allow at least 1% of UV radiation to penetrate skin.
  • You have not applied the correct amount of sunscreen and are therefore not receiving the SPF/UVA-PF you think you are.
  • You have not reapplied your sunscreen frequently enough – sunscreen can only absorb UV radiation for a limited period of time before it needs to be reapplied.
  • Your sunscreen does not offer adequate UVA protection or the ratio of UVA to UVB protection is unbalanced – SPF50 may let you receive 50x the amount of UVB radiation before burning but PA++++ only lets you receive 16x the amount of UVA radiation before tanning.

So even if you apply enough sunscreen with adequate UVA protection and reapply it frequently enough, you are still likely to get a slight tan. Practicing sun-safe behaviors alongside daily sunscreen use will offer you the best chance of protection.

Such sun-safe behaviors include:

  • Avoiding midday sun (between the hours of 11 am-3 pm) when UVB radiation is at its strongest.
  • Seeking shade where possible.
  • Wearing hats, sunglasses, and other protective clothing when in the sun.
  • Avoiding sun-bathing altogether.

Plus, as has already been mentioned:

  • Apply the recommended amount of sunscreen (2mg/cm2)
  • Reapply sunscreen regularly (every 2hrs)
  • Opt for sunscreens with high UVA protection

 

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Laura is a skincare addict and sunscreen enthusiast with more than 10 years of experience working in healthcare and over 5 years of experience working as a nurse. She has experience in plastic and reconstructive surgery, dermatology, and aesthetics and has received training in laser treatments. Laura is currently working in healthcare education and writes for ScienceBecomesHer in her spare time. Read More.

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