Middle and far infrared studies of the irregular galaxy M 82 and of Seyfert galaxies are presented. M 82 was observed spectrophotometrically from 8 to 13 microns at 6 different positions selected across its 10 microns emitting region. A model is proposed which explains satisfactorily most of the observed properties of M 82 from X-ray to radio wavelengths. It is also suggested that a similar model may be applied to other active nuclei, like the emission line alaxy NGC 1614 and the classical Seyfert 1 galaxy NGC 7469. The far IR emission from Seyfert galaxies was also studied. Data analyzed are drawn from the recently released IRAS catalog. Seyfert galaxies are strong far infrared sources, but unlike the near and mid IR emission from these sources, the far IR emission does not appear to be produced by the active nucleus. Seyfert galaxies are depicted as composed of an active nucleus that powers the near and mid IR, plus a galactic envelope that supports the starburst episodes.