Recent observational results obtained with SCUBA , COBE and ISO have greatly improved our knowledge of the infrared and sub-mm background radiation .
These limits become constraining given the realization that most AGNs are heavily obscured and must reradiate strongly in the IR/sub-mm .
Here we predict the contribution of AGNs to the IR/sub-mm background , starting from measurements of the hard X-ray background .
We show that an application of what we know of AGN Spectral Energy Distributions ( SEDs ) and the IR background requires that a significant fraction of the 10-150 \mu m background comes from AGNs .
This conclusion can only be avoided if obscured AGNs are intrinsically brighter in the X-rays ( with respect to the optical-UV ) than unobscured AGNs , contrary to “ unified schemes ” for AGNs , or have a dust to gas ratio much lower ( \leq 0.1 ) than Galactic .
We show that these results are rather robust and not strongly dependent on the details of the modeling .