Most “sunscreen failures” happen for one reason: we don’t put enough on, and we don’t reapply often enough. (1–4)
This guide shows you exactly how much to use, where to put it, and when to reapply — so the SPF on the label has a chance of being the SPF on your skin.
Book a 20 minute appointment with Dr Chris (Sun protection plan + sunscreen advice)
Want the label basics first? (UVA vs UVB, SPF and broad-spectrum explained)
Key takeaways
- Apply sunscreen 20 minutes before you go outdoors. (1–3)
- Reapply every 2 hours while outdoors, and after swimming, sweating, or towel-drying. (1–4)
- An average adult needs about 7 teaspoons (≈35 mL) for full body coverage. (1–3)
- Under-applying drops protection far more than people expect — the relationship is not linear. (5)
- Sunscreen works best with hat, clothing, shade and sunglasses. (1,2)
Step 1: Put it on early (timing matters)
Apply sunscreen to clean, dry skin at least 20 minutes before sun exposure. (1–3)
This gives it time to form a more even protective film and reduces the “slap it on at the beach” problem.
If you’re going out later, make it a routine:
- sunscreen on after morning skincare
- then breakfast / packing / commute
- then outdoors
Step 2: Use enough (the teaspoon rule)
Cancer Council guidance is simple and practical: an average-sized adult needs about 7 teaspoons (≈35 mL) for a full body application. (1–3)
The 7-teaspoon rule (average adult)
- 1 teaspoon: face, neck and ears
- 1 teaspoon: each arm (2 total)
- 1 teaspoon: each leg (2 total)
- 1 teaspoon: front of torso
- 1 teaspoon: back of torso
Total: 7 teaspoons (≈35 mL) (1–3)
If you’re taller, broader, or very muscular, you’ll usually need more than 7 teaspoons to cover everything evenly.
If you only sunscreen “a bit”, you’re usually getting “a bit” of the SPF.
Step 3: The two-finger method (easy for face and neck)
If teaspoons feel fiddly, there’s another practical way to estimate dose.
Medical literature describing sunscreen dosing notes that 2 mg/cm² (the standard test thickness) can be approximated by two finger lengths of sunscreen for each body area (when dividing the body into standardised regions). (6)
A patient-friendly version many people use:
- Face + neck: two finger lengths (index + middle finger)
If you’re not sure which method you’ll actually follow, choose the one you’ll use consistently.
Step 4: Don’t miss the “high-risk” zones
The most commonly missed spots are also high-risk for skin cancer and sun damage:
- ears (front and back)
- back of neck
- scalp part line / hairline
- tops of feet
- backs of hands
- along the jawline and under the chin
- around sunglasses lines and nose folds (7)
If your doctor has commented on early sun damage or actinic keratoses, it often starts in places like the ears, hands and nose. (Actinic Keratosis)
Step 5: Reapply properly (this is where people fall down)
Even the best sunscreen film breaks down in real life: rubbing, sweating, swimming, towelling, and uneven coverage all reduce protection.
Guidance is consistent across Australian authorities:
- reapply at least every 2 hours while outdoors
- reapply after swimming, sweating, or towel-drying (1–4)
Practical tip: set a phone alarm if you’re outside for more than 2 hours.
If you work outdoors or train hard: (Sunscreen for outdoor workers and athletes)
Important: under-application drops SPF sharply (not linearly)
This is the part that changes behaviour.
Research shows the relationship between how much sunscreen you apply and the SPF you actually receive follows an exponential pattern. (5)
In one well-cited in-vivo study, applying half the test thickness dropped the measured SPF to roughly the square root of the labelled SPF. (5)
What this means in practice:
- If you apply a very thin layer, your “SPF 50+” may behave much closer to single-digit SPF. (5)
This is a major reason we commonly recommend SPF 50+: it gives more margin for error — but only if you still apply a generous amount and reapply. (2,5)
Sunscreen with skincare and makeup
Order of application (simple version)
- moisturiser (if you use it)
- sunscreen
- makeup (if you wear it)
This is great and if applied correctly will give you SPF50+ protection… for two hours. For most working women while still a great start this means your protection will start weaning between 9-10am, and be negligible when you need it most for the coffee break or lunch cafe visit. See my below thoughts on how to best manage with this but honestly you need to mainly rely on other forms of protection while wearing make-up for more than 2 hours – hats, sunglasses and shade.
Reapplying over makeup (realistic options)
If you’re outdoors for hours, you still need to reapply. Choose the method you’ll actually do:
- reapply a lotion sunscreen by gently pressing it on with a sponge (least “pretty”, most reliable)
- Many of my patients use ‘sunscreen spritz’ – while technically SPF50+ there is almost no way you are putting enough on. More likely you will be achieving closer to SPF4-5. If you use this method “Spray, Rub, Repeat” method:
a.Spray until the skin looks glistening/wet.
b.Rub it in thoroughly with your hands to fill the gaps.
c.Repeat a second layer to ensure you’ve hit the required thickness. (still unlikely but at least you’re trying!)
- use a sunscreen stick for targeted areas (nose, cheeks, forehead)
- use protective clothing/hat/shade
Makeup with SPF in it is better than nothing, but most people do not apply makeup thickly enough to achieve the labelled SPF in real life. (6)
If you’re pigment-prone: (Tinted sunscreen and visible light for pigmentation)
Sprays, aerosols, and “easy” sunscreen
Aerosol/spray sunscreens are popular because they feel quick — but they are harder to apply evenly.
Cancer Council has advised that aerosol sunscreens are difficult to apply correctly and has urged Australians to prefer creams and lotions for more reliable coverage. (8,9) ARPANSA has also reported concerns about coverage reliability with aerosols. There are also some health concerns with accidental inhalation of sunscreens(10).
If you use a spray anyway:
- spray generously
- rub it in to even the film
- avoid spraying directly onto the face (spray into hands first)
For families and kids guidance: (Sunscreen for babies, kids, pregnancy and breastfeeding
Sunscreen is one pillar, not the whole plan
The best “sunscreen” is still: shade + clothing + hat + sunglasses + sunscreen. (1,2)
If you have significant sun damage, many actinic keratoses, or a history of skin cancer, sunscreen is essential — but prevention often includes:
- (Full Skin Checks)
- (Actinic Keratosis Treatment)
- (Efudix (5-fluorouracil))
- (Laser-assisted photodynamic therapy (LA-PDT) for non-melanoma skin cancer)
Frequently asked questions
How much sunscreen should I use on my face?
About 1 teaspoon for face/neck/ears (or the two-finger method for face/neck). (1–3,6)
Do I really need to reapply every 2 hours?
Yes, if you’re outdoors. Reapply every 2 hours and after swimming, sweating, or towel-drying. (1–4)
My sunscreen says “4 hours water resistant” — can I wait 4 hours?
No. Water resistance does not replace reapplication, especially with towelling, sweat, and friction. (3,4)
Can I use sunscreen once in the morning and be covered all day?
Not reliably. Sunscreen film breaks down and is often applied unevenly. Reapply. (1–4)
What matters more: SPF number or how I apply it?
For most people, how you apply and reapply has the biggest impact on real-world protection. (1–5)
I keep missing spots — what should I focus on?
Ears, neck, scalp part line, hands, nose, and tops of feet. (7)
Book a sunscreen and sun-damage prevention review
If you’re outdoors a lot, burn easily, are pigment-prone, or have sun damage/actinic keratoses, we can tailor a plan you’ll actually stick to.
Book a 20 minute appointment with Dr Chris (automed 20 minute (Sun protection plan + sunscreen advice))
Or start with a full risk assessment: (Full Skin Checks)
References
1.Cancer Council Australia. Be SunSmart (guidance includes applying sunscreen 20 minutes before exposure; 7-teaspoon rule; reapply every 2 hours and after swimming/sweating).
https://www.cancer.org.au/cancer-information/causes-and-prevention/sun-safety/be-sunsmart
2.Cancer Council Australia. Five SunSmart steps (Slip, Slop, Slap, Seek, Slide) (7 teaspoons for full body; sunscreen as one part of sun protection; timing).
https://www.cancer.org.au/save-your-skin/five-sunsmart-steps
3.Cancer Council (Shop / consumer guidance). How to apply sunscreen (≈35 mL; teaspoon per body part; apply 20 minutes before; reapply every 2 hours / after swimming/sweating/towel drying).
https://www.cancercouncilshop.org.au/pages/how-to-apply
4.ARPANSA. Sun protection using sunscreens (reapply every two hours; after swimming; sunscreen is wiped off/lost through perspiration; purpose is to reduce UV exposure not extend time outside).
https://www.arpansa.gov.au/understanding-radiation/radiation-sources/more-radiation-sources/sun-protection-sunscreen
5.Faurschou A, Wulf HC. The relation between sun protection factor and amount of sunscreen applied in vivo. Br J Dermatol. 2007 (SPF vs quantity follows exponential growth; 1 mg/cm² ≈ square-root fall; 0.5 mg/cm² ≈ fourth-root).
https://pubmed.ncbi.nlm.nih.gov/17493070/
6.Taylor S, et al. “SunSmart Plus”: the more informed use of sunscreens. Medical Journal of Australia. 2004 (discussion of dosing concepts; 2 mg/cm² and practical dosing approximations including finger-length guidance).
https://www.mja.com.au/journal/2004/180/1/sunsmart-plus-more-informed-use-sunscreens
7.Cancer Council Victoria. Australians don’t apply enough sunscreen (teaspoon rule and missed-spot messaging; practical guidance).
https://www.cancervic.org.au/get-support/stories/australians-dont-apply-enough-sunscreen.html
8.Cancer Council Australia. Sunscreen fact sheet (National Cancer Prevention Policy Skin Cancer Committee resources) (notes difficulty applying aerosol sunscreen correctly; product standards guidance).
https://www.cancer.org.au/about-us/policy-and-advocacy/prevention/uv-radiation/related-resources/sunscreen
9.Cancer Council Australia. Media release: strongly urges Australians against aerosol sunscreens (prefers lotions/creams for easier, more reliable application).
https://www.cancer.org.au/media-releases/2022/cancer-council-strongly-urges-australians-against-aerosol-sunscreens
10.ARPANSA. Aerosol sunscreens inadequate for UV coverage (coverage reliability concerns; reinforces 20 minutes before and two-hourly reapplication messaging).
https://www.arpansa.gov.au/news/aerosol-sunscreens-inadequate-uv-coverage