If these are newer brand-name fixtures (20 years or so) they mostly use a ceramic cartridge. Rubber seals in those do wear out over time.
Turn off the water to the faucet. Remove the handle, unscrew or unclip the cartridge, replace with a new one. If you take the cartridge to your hardware store they should be able to match it with one they have.
Each brand is a little different and if you can determine the brand it may be a good idea to do a search on-line for how to change your faucet cartridge, especially if this is your first time.
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Take it apart, clean out the gunk and install a new washer.
If these are newer brand-name fixtures (20 years or so) they mostly use a ceramic cartridge. Rubber seals in those do wear out over time.
Turn off the water to the faucet. Remove the handle, unscrew or unclip the cartridge, replace with a new one. If you take the cartridge to your hardware store they should be able to match it with one they have.
Each brand is a little different and if you can determine the brand it may be a good idea to do a search on-line for how to change your faucet cartridge, especially if this is your first time.