  The chemical influence of luminosity outbursts on the environments of young
solar-type stars is explored. Species are categorised into several types
according to their response to the outburst. The first and second types imply
chemical changes only during the outburst (with slightly different behaviours).
These response types are mostly observed close to the star and are caused by
icy mantle evaporation. However, mantles recover after the outburst almost
immediately. A notable exception is benzene ice, which is accumulated on dust
surfaces during and after the outburst, so that its abundance exceeds the
pre-outburst level by orders of magnitude. The third type of response is mostly
seen at the disc periphery and implies alteration of abundances during the
outburst and preservation of these `abnormal' abundances for centuries. This
behaviour is typical of organic compounds, like HCOOCH$_3$, CH$_3$CN, CH$_2$CO.
Their presence in the dark disc regions can be a manifestation of the past
outburst. CO and CO$_2$ only trace past outbursts at the remote disc regions.
The outburst changes the C/O ratio, but it quickly returns to the pre-outburst
value almost everywhere in the disc. An important factor determining the
sensitivity of molecular composition to the outburst is the dust size
distribution. The duration of the pre-outburst stage and of the outburst itself
influence the chemical effects, if the burst duration is shorter than 50 yr and
the duration of the quiescent phase between the bursts is shorter than 100 kyr.
