Bear spray expiry dates debunked: capsaicin stable, weight check valid, study flawed
Your bear spray might last years longer than the label says — here's the real science.
A curious outdoors enthusiast investigated whether bear spray expiry dates are meaningful after a 4-year-old can sat unused. The good news: capsaicin, the active ingredient, does not degrade over time. The primary failure mode is propellant leakage, which is easily checked by weighing the can—if it drops below 75% of its original weight, it's compromised. The author's can still weighed 300g after four years (original: 300g), and a test spray worked as expected, suggesting the can could last up to a decade with annual weight checks.
However, the investigation uncovered a startling piece of pseudoscience. A 2020 paper in the Journal of Wildlife Management by Brigham Young University researchers claimed that bear spray pressure declines logarithmically, with half the spray lost in the first second. This directly contradicts abundant video evidence of cans spraying evenly until empty. The paper's authors apparently ignored their own filmed trials, leading the author to conclude it's a textbook example of peer-reviewed nonsense. The real takeaway: expiry dates are mostly about propellant integrity, not active ingredient degradation, and users can safely extend can life by simple weight checks.
- Capsaicin does not degrade; the main expiry risk is propellant leakage, detectable by weighing the can.
- A 4-year-old bear spray can still produced a vigorous 5-6 meter stream with no pressure drop.
- A 2020 peer-reviewed study incorrectly claimed logarithmic pressure loss, contradicting real-world tests and basic aerosol physics.
Why It Matters
Save money and reduce waste by ignoring arbitrary expiry dates—simple weight checks can extend bear spray life.