The climate crisis is making people sicker—worsening illnesses ranging from seasonal allergies to heart and lung disease. Children, pregnant people and the elderly are the most at risk from extreme weather and rising heat.  As temperatures increase, plants produce more pollen for longer periods of time, intensifying the allergy seasons. Increased concentrations of carbon dioxide in the atmosphere can make plants grow more and cause more grass pollen, which causes allergies in about 20% of people. Carbon dioxide can also increase the allergy-causing effects of pollen. We’re finding that we have increasing numbers of children born already in a weakened state from heat and air pollution. Air pollution gets worse as temperatures rise, stressing both the heart and lungs. The fossil fuel pollution that causes the climate crisis also is linked with increased hospitalizations and deaths from cardiovascular disease, and it is connected with more asthma attacks and other breathing problems. Children under the age of five experience the majority of the health burden from climate change. Higher temperatures and the depletion of the ozone layer increase the risk of skin cancer. The same refrigerants and gases that damage the ozone layer contribute to climate change. Heat is linked with higher risks for salmonella and campylobacter outbreaks. Extreme rains can contaminate drinking water. Harmful algae blooms that thrive in higher temperatures can cause gastrointestinal problems, too. People exposed to or displaced by extreme weather or violent conflict are at higher risk for mental health challenges. Extreme heat can also make some mental illnesses worse. Fossil fuel pollution can increase the risk of stroke. Coal combustion also produces mercury—a neurotoxin for fetuses. Diseases spread by mosquitoes and ticks increase the chance of neurological problems. Extreme heat is also linked with cerebrovascular disease, a disorder that affects blood supply to the brain.