Forest fires and other environmental pollutants contribute to unhealthy air quality due to small particles in the air. These microscopic particles enter the lungs and cause health problems including asthma exacerbations and decreased oxygenation in addition to long term harm such as cancer. Individuals with heart and lung disease, elderly individuals, as well as children and adolescents are at increased risk from exposure. Monitoring the air quality index can help guide decisions about outdoor activities during times of increased risk. At levels over 100 at risk individuals should restrict time outdoors or use particle filtering masks such as n95s. At levels over 300 everyone should head indoors to reduce risks.