The effect of altitude on boiling point is primarily due to the decrease in atmospheric pressure at higher elevations. As altitude increases, the pressure exerted on a liquid decreases, which allows it to boil at a lower temperature. For instance, water boils at about 100°C at sea level but can boil at around 90°C or lower in high-altitude areas like mountainous regions. This phenomenon has practical implications for cooking and baking, where adjustments in temperature and cooking time may be necessary at higher altitudes.