First advanced by Paul Vignon in 1902 it assumes the image was caused by the projection of body vapours. The phenomenon would result from the sweat urea decomposing in ammonium carbonate then becoming carbon dioxide, water and ammonia; the next chemical reaction with aloe and myrrh, used for the burial, would produce a colorimetric variation.

This theory was criticized a lot; the main objections are:

-   the transformation of aloe in ammonium carbonate does not happen immediately after death (even if aloe and myrrh can accelerate it);

-   the cadaverous vapours do not produce such constant and precise effects enabling to "designe" such a refined image like the one of the man of the Shroud;

-   the vapours post-death diffusion is never orthogonal but distributed in many directions;

-   the quantity of sweat urea evaporated from the cadaverous skin could hardly have been dense enough to influence the reaction necessary to create such wide impressions.