You've heard it once, you've heard it a million times. SPF is the most important step in your skincare and makeup routine. That much is clear.

But when we start actually looking at SPF products, that's where it gets a little murky. Many skincare and makeup products claim to contain SPF 15, 20 or sometimes even 30. But the benefit of the SPF isn't always what it claims to be - particularly in makeup.

We spoke to Isabella Loneragan, one of Australia's leading skincare experts and founder of The Dermal Diary to find out more. She answered all our questions on how SPF works in makeup and how to reapply if we need more.

Let's start from the beginning, can you explain SPF? What does it mean?

SPF stands for Sun Protection Factor and it indicates the level of protection against ultraviolet B rays (UVB), these rays are what cause sunburn. You will find an SPF rating on any suncream on the market, the higher the SPF rating, the more protection your skin will have from the sun’s UV rays.

How can SPF protect you from the sun? Is it about increasing the time before you start to burn?

The number in SPF tells you how long the sun's UVB rays would take to redden your skin if you apply the sunscreen exactly as directed compared with the amount of time without sunscreen.

How long does an SPF last?

This really depends on what you are doing for the day, if you apply your sunscreen in the morning and spend the whole day inside, your SPF would last you until you get home. Although, if you are spending the whole day outside you should be reapplying sunscreen every 2 hours. SPF’s efficiency is not dependent on time as such but on how long your skin is exposed to the UV rays.

Does an SPF in your makeup actually do anything?

Short answer yes, as any form of SPF will help protect your skin from sun damage. But, due the low amount of SPF in most makeup products it may not be enough to protect you adequately.

Should we be using an additional SPF?

Yes! Even though your makeup may say SPF is included, this does not necessarily mean that it will be adequate coverage. Most cosmetic companies put minimal sunscreen into products, just enough for them to claim that there is SPF in the product. You’d most likely need to use A LOT of product to adequately protect your skin, resulting in wasting product when you could just be using a less of a separate product. Unless of course you are using a great BB cream like our Glow Getter that contains ample SPF 30+ and also acts as a primer and tinted moisturiser.

How can you reapply if you’re wearing makeup?

Keep a makeup sponge handy at all times, use this to apply a BB cream with SPF like the Glow Getter and dab all over your face and neck. This is perfect for reapplying due to the tint in the BB cream, keeping you protected from the sun whilst still keeping your makeup intact.