Treat it as a possible gas leak first. Natural gas has no smell of its own, so utilities add an odorant that many people describe as skunk or rotten eggs. If the smell is strong or near a gas appliance, leave the house and call 911 or your gas company from outside. Sewer gas comes next.
Do not flip switches or use a phone inside if you suspect gas. Once gas is ruled out, the next likely source is sewer gas. Every drain holds water in its trap, and that water blocks gas coming up from the sewer. When a trap dries out in a guest shower, a floor drain, or a sink nobody uses, sewer gas comes straight into the room. A failed toilet wax ring or a cracked vent pipe does the same.
DFW heat evaporates trap water faster than most homeowners expect. A shower left unused for a few summer weeks can go dry. The smell often comes and goes with weather and airflow.
Pour a quart of water into every floor drain and unused fixture. If the smell fades within a day, a dry trap was the cause. If it stays, the problem sits in the pipes: a broken vent, a failed seal, or a cracked line under the slab. Sometimes it is an actual skunk under the house or near an air intake, which no plumber can fix.
Nuflow DFW is a licensed trenchless sewer contractor serving 25 Dallas-Fort Worth cities, RMP# 46694. A camera inspection finds the cracks and failed joints that let sewer gas in. You keep the footage. Call (469) 701-0597.