Optimal carnot efficiency := 1 - T_u/T_o. So for about 10 K difference, you will end up with max. efficiencies of some 3 %. But don't catch a cold since the heat will have to be drawn from your skin in a substantial amount, if the value of the collected energy is to rise beyond, say, 10 Cents/day.
You still need to dump the heat effectively, so even a Peltier element may need its 'cold' side to be a fan-blown heatsink. The 'hot' side is going to be neither comfortable nor simple to 'attach' to the body.
What is the desired use for this power, and can it be provided through mechanical energy scavenging systems?