How do we know that sin is the cause of sickness?

Sin is fundamentally the cause of all sickness and death according to Scripture. Romans 5:12 explains that sin entered the world through one man, Adam, resulting in death spreading to all men because all have sinned. This universal condition means that sickness is a part of the human experience due to our fallen nature. Furthermore, 1 Peter 5 reminds us that we will face trials and afflictions, not necessarily as punishments, but as part of our sinful condition. This isn't to assert that every illness is a direct punishment for a specific sin, but rather that our collective sin nature results in the sickness we experience in a fallen world.