Experts Tailor SPF 30 Reapplication Advice Beyond 2-Hour Rule

Q: Why might that expensive bottle of sunscreen sitting in your beach bag already be completely useless?

It may already be useless if it is expired or has been damaged by heat and sun in your beach bag. Sunscreen is regulated like a drug, and experts say its UV filters and preservatives can break down over time, especially if the bottle has been left in direct sun, a hot car, or a bag that heats up for hours. That matters because degraded sunscreen may no longer deliver the SPF on the label. FDA guidance says products without an expiration date should generally be treated as expired three years after purchase. Even before that, poor storage can shorten its life. A bottle that looks normal can still be less reliable if it has spent a season baking in heat. There are also visible warning signs. If the sunscreen has separated, become clumpy or gritty, changed color, or smells sour or unusual, experts say it should be thrown out. Those changes suggest the formula has broken down and may not spread evenly or protect properly. Even a fresh sunscreen can be ineffective if too little is applied. Dermatologists and sunscreen specialists say underapplying is one of the most common mistakes, especially with sprays, which can miss spots or go on too thin in windy conditions. Lotion is often easier to apply evenly, and reapplication matters more when swimming, sweating, or spending long periods in strong sun. In short, a pricey bottle in your beach bag may be useless not because of the brand, but because it is old, heat-damaged, or being applied too sparingly to work as intended.

3 articles · Updated · National Post · Aug 2

Health Canada still advises broad-spectrum SPF 30 sunscreen 15 minutes before sun exposure and reapplication every two hours, but dermatologists say that interval can stretch when people are inactive, shaded and not sweating or swimming.
Dr. Cheryl Rosen said reapplication matters more during high-exposure activities such as swimming, water skiing and heavy sweating, while winter use may be limited mainly to exposed areas like the face during skiing.
One teaspoon per exposed body part remains Health Canada’s guide, though KINeSYS founder Lisa Heggie said the right amount varies with body size, exposed skin and sun-protective clothing.
Lotion and pump sprays can deliver more even coverage than aerosol sprays, Heggie said, because wind and uneven application can leave users below the SPF protection stated on the label.
Hats and UV shirts can reduce how much skin needs sunscreen, reinforcing the broader message that protection should match activity, season and surroundings rather than follow a rigid schedule.