A leaking kitchen faucet is usually caused by a worn cartridge, damaged O-ring, or a loose internal connection. Here's how to fix it yourself.
Locate the shutoff valves underneath the sink and turn them clockwise until fully closed. Open the faucet to release remaining pressure.
Find the set screw on the handle. Use the correct Allen key to loosen it, then lift the handle off carefully.
Remove the cartridge. If cracked, worn, or stiff, replace it. Inspect O-rings — if flattened or brittle, replace them. Apply plumber's grease before reinstalling.
Reinsert the cartridge, reattach the handle, and tighten the set screw. Slowly reopen the shutoff valves and check for drips around the handle and base.