Chitosan derivatives as soil release agents

A washing agent or laundry post-treatment agent comprising a chitosan derivative having a modified anhydroglycoside unit of general formula (I),

• wherein:
• the functional groups R are selected, independently of one another, from the group consisting of —H, —(CH2)mSO3H and —(CH2)mSO3−X+,
• m represents a number from 1 to 3,
• X+ represents a charge-balancing cation,
• at least one of the functional groups R is not —H, and
• the average degree of substitution in the chitosan derivative is from 0.1 to 1.0, based on the proportion of functional groups —NR2 which are not —NH2;
• wherein the chitosan derivative is present in an amount of from 0.1 wt. % to 3 wt. %, based on the total weight of the washing agent or laundry post-treatment agent.