# From what wavelength can radiation go through a human body without very much changing?

Gamma-rays can go through a body but they will ionize a lot of atoms (I don't know whether some of the gamma photons will go through without any interaction at all?). The same for X-rays. Visible light and infrared (till $1mm$) probably only reflects and absorbs. But perhaps rays from 1 cm and longer (radiowaves) can get through the human body without harming the body or without changing in frequency?

• Penetration depth decreases with increasing frequency. Here is a PhD thesis on the subject. – lemon Feb 24 '16 at 11:03
• Your microwave oven has a frequency of approx. 2.4GHz and a wavelength of approx. 12cm and that wavelength will definitely get absorbed by your body really well. There are national and international em radiation limits at basically all frequencies almost all the way to DC and with good reason. The human body does absorb and will be affected at essentially all frequencies. – CuriousOne Feb 24 '16 at 11:06