What causes a sewage smell to come from kitchen sink?

this should not be happening that is what a ptrap is for…. you know the curve in the pipe under the sink …it keeps gasses from coming through…. make sure there is a trap down there if not install one other wise keep the bleach handy good luck from TEXAS

my guess would be you have a air lock some where in your drain line run your sinks 3/4 full and let the water out starting with the up stairs first and go down from there if this does not work use a 1/2 cup bleach in each sink and let stand in the drain for 30 min. and flush with cold water

usually smells start in the shower drain but if it is only in the kitchen drain I would pour a box of baking soda into the drain. let it sit then as it goes down the drain it takes the odors with it. If it is extreme Mr. Rooter Plumbing has a biodegradable product called BIO-choices which is economically safe and sponsored by the EPA. It is expensive but it lasts a long time. It is not harmful to septic systems either…worth looking into.

Do you have a dishwasher? If so, an accumulation of grease and food in the discharge hose between the air-gap and the dispoze-all is very common, especially true if that black discharge hose is kinked or too long and ‘bellies’ down, so that there’s always funky water/crud in it. Another source is a partially-clogged P-trap under the sink. These are about a difficulty-rating of 2 or 3 on a 1-to-5 scale. Or call a licensed plumber or handyman, all done in less than an hour. The downstairs sink may be the problem, so it will take a little detective work. A temp fix is pouring a citrus-based cleaner into the sink drains and letting it sit in the drain for as long as possible: I like the “ZEP Citrus Cleaner” at Home Depot.