The Battlesnake Royale map was the first to introduce a new danger, called Hazards.
Hazards slowly encroach from the edges of the game board every 25 turns, creating an ever-shrinking 'safe zone'. Entering a grid location marked as a Hazard will cost 14 health, in addition to the loss of 1 health per turn.
Food can spawn inside and outside of the Hazard area. If a Battlesnake consumes food inside a Hazard location, it will receive the full benefits of the food and not be penalized for entering the Hazard.
Hazards that spawn in a location that a Battlesnake has just moved into will have no effect — Hazard damage is only applied on subsequent turns after their initial spawn, and your Battlesnake will have an opportunity to leave the location before taking damage.