Are duck down pillows harmful to the human body?

Yes.

Improper filling of duck down pillows can lead to insufficient neck support, increase pressure on the cervical spine, and cause damage to the cervical spine after long-term use. Duck down pillows that have not been properly treated and cleaned can cause allergic reactions or bacterial growth that can lead to skin infections. When choosing a duck down pillow, you need to choose a pillow that is properly filled and properly processed, and clean and replace the pillow core regularly.