Hello Fausto,
First of all my apologies for late response. I think there is a misunderstanding in the concept/working of TMP006 here. Die temperature is not used as a reference for measurements. Die temperature and thermometric voltage are used in calculating the Object temperature. You will be needing an additional temperature sensor (other than die temperaure) for reference measurements. I would suggest using an accurate reference temperature sensor for this, since you are trying to calibrate TMP006 for the skin.
Since human skin has high emissivity we use a black body reference to calibrate TMP006 for human skin temperature measurements.
If you have any further questions please don't hesitate to email me directly (abhishekmuppiri@ti.com). Also if you can send me pictures of your setup, it would help me with my understanding.
Best Regards,
Abhi