This guide is for general information only and is not legal advice. Laws change — verify current rules with your state DOT or a licensed attorney before relying on this for any legal matter. Read full disclaimer.
The rule
Pennsylvania requires a bicycle helmet for any rider under the age of 12. The same rule extends to children carried as passengers in a child seat or trailer. Summary offense; fine of up to $25, often waived on proof of helmet purchase. See 75 Pa. Cons. Stat. § 3510.
If you're 12 or older, Pennsylvania doesn't require you to wear a helmet by state law. Riders under 12 (and any child carried as a passenger) must wear a helmet that meets the ANSI/Snell/ASTM (federally superseded by CPSC for any helmet sold in the US since 1999) standard.
Cities can be stricter than the state floor, and bike-share systems often require helmets regardless of age. If you're renting or commuting in a major city, confirm the local rule before you ride.