We point out that the non-gaussianity arising from cubic self interactions of the inflaton field is proportional to \xi N _ { e } where \xi \sim V ^ { \prime \prime \prime } and N _ { e } is the number of e-foldings from horizon exit till the end of inflation .
For scales of interest N _ { e } = 60 , and for models of inflation such as new inflation , natural inflation and running mass inflation \xi is large compared to the slow roll parameter \epsilon \sim V ^ { \prime 2 } .
Therefore the contribution from self interactions should not be outrightly ignored while retaining other terms in the non-gaussianity parameter f _ { NL } .
But the N _ { e } dependent term seems to imply the growth of non-gaussianities outside the horizon .
Therefore we briefly discuss the issue of the constancy of correlations of the curvature perturbation \zeta outside the horizon .
We then calculate the 3-point function of the inflaton fluctuations using the canonical formalism and further obtain the 3-point function of \zeta _ { k } .
We find that the N _ { e } dependent contribution to f _ { NL } from self interactions of the inflaton field is cancelled by contributions from other terms associated with non-linearities in cosmological perturbation theory .

Keywords : Inflationary cosmology , non-gaussianity , curvature perturbation