Poison Master( Complete Scoundrel, p. 80)
The toxins you create and use are particularly virulent.
Choose a type of poison (contact, ingested, inhaled, or injury) for which you have selected the Poison Expert feat. The initial and secondary damage dealt by poisons of this type that you create and use increases by 1 point per die of damage (or by 1 point, if it deals a fixed amount of damage). For example, lich dust used by a character with Poison Master (ingested) would deal initial damage of 2d6+2 Str and secondary damage of 1d6+1 Con plus 1d6+1 Str. If a poison doesn't deal damage, this feat has no effect.
This feat has no effect on poisons used by other creatures, even if you craft those poisons. It also has no effect on natural poisons (those exuded from a creature's body).
You can gain this feat multiple times. Its effect does not stack. Each time you take the feat, it applies to a different type of poison for which you have selected Poison Expert.