Choose a caulk that is designed both for bathrooms and for mildew resistance.
Silicone a shower door.
Once you have removed all large pieces go back and check that you have adequately cut out all discolored sealant.
Caulk made of pure silicone or siliconized latex acrylic i e latex or acrylic caulk with added silicone adheres well to common shower and tub materials including porcelain ceramic stone.
Start with the knife and carefully begin to cut away at silicone around shower enclosure making sure not to scratch.
Next spray the glass cleaner of your.
Silicone caulk forms a stronger seal than latex caulk but latex caulk is easier to clean and remove if the seal fails.