Why is being underweight a hazard to health?

Being underweight can pose significant health risks, including weakened immune function, increased susceptibility to infections, and nutrient deficiencies that can lead to anemia and other health issues. It may also result in decreased muscle mass and bone density, increasing the risk of fractures and osteoporosis. Additionally, being underweight can affect overall energy levels and lead to fatigue, impacting daily functioning and quality of life.