Phil Plait in Bad Astronomy:
Homeopathy is the antiscientific belief that infinitely diluted medicine in water can cure various ailments. It’s perhaps the most ridiculous of all “alternative” medicines, since it clearly cannot work, does not work, and has been tested repeatedly and shown to be useless.
And for those who ask, “what’s the harm?”, you may direct your question to Thomas Sam and his wife Manju Sam, whose nine-month-old daughter died because of their homeopathic beliefs.
The infant girl, Gloria Thomas, died of complications due to eczema. Eczema. This is an easily-treatable skin condition (the treatments don’t cure eczema but do manage it), but that treatment was withheld from the baby girl by her parents, who rejected the advice of doctors and instead used homeopathic treatments. The baby’s condition got worse, with her skin covered in rashes and open cracks. These cracks let in germs which her tiny body had difficulty fighting off. She became undernourished as she used all her nutrients to fight infections instead of for growth and the other normal body functions of an infant. She was constantly sick and in pain, but her parents stuck with homeopathy. When the baby girl developed an eye infection, her parents finally took her to a hospital, but it was far too late: little Gloria Thomas succumbed to septicemia from the infection.
More here.