The best mildew remover I have found is a brand called K-14.
I can find it at my grocery store and the hardware store. I ignore the directions---just spray it on lavishly and walk away. Be careful of your clothes and carpet---it is VERY strong stuff. Best to do it after the shower before you are dressed. And hold a rag under the spray bottle for drips.

I've always found that this is a situational thing. My answer depends upon how much mildew that you're talking about and if you're really sure that it's the grout and not caulking that's affected.

For mild cases of either type (surface, not entrenched), I use Tilex and let it sit. If it's mild, you should be able to walk away, come back in about 30 minutes and it should be gone.

If it's caulk and it's entrenched, replace the caulk. There is a certain point where it's deep in the stuff and no voodoo will get it out.

If it's tile and Tilex doensn't work, you can try pure bleach. If that doesn't work, you're talking having to use a professional grout cleaner which is very caustic and beyond my knowledge. If it were me, I'd be going to Home Depot or some place like it and asking for help and advice on which product to use. For something like that, make sure that you wear old clothing and use thick rubber gloves. I saw my mother rip her knees to shreds with teh stuff because she was kneeling and doing her kitchen floor with the stuff and it soaked into the knees of her jeans. Severe chemical burns. Nasty stuff, so be careful.

Try a hand steamer - like Hot Shot.
The real problem is two fold - your grout is not sealed properly and you may not have adequate air ventalation.
Grout Sealer can be used when the grout is completely dry - you really should wait 5 days after cleaning it. Preferably after you have been out of town, not using the area. Get Aquamix Gold at HD and a cheap sponge paint applicator.
Check the air ventalation.
Good Luck!

Be very careful what you use won't discolor your tiles. I have charcoal grey grout and have given up trying to clean it. (it is white with soap scum and looks awful) I damaged some of my tiles using some of the grout cleaning products.

What I am going to do is get a grout colorant/sealer and just repaint the grout. Hopefully, if it is also sealed, it will be easier to clean in the future.

K-14 is MUCH stronger than Tilex. I have used it only on white grout and sealer. And it is great for cleaning those cheap white plastic patio chairs and table.

Try a clorox bleach pen. They are amazing! Then seal your grout!

This is an old "Hints by Heloise" trick. Spray or wipe on pure bleach to take out the black color...rinse...let dry and then use pure ammonia to kill the mold/mildew spores. Have plenty of ventilation and use rubber gloves. Hope everyone knows not to mix the two...produces a very harmful gas.

As was mentioned above...it won't work if the mold/mildew is imbedded or covered over with a clear sealant.

I've had good luck with Oxyclean, recommended by the guys over in the bathroom and deck forums. I mix it up in a small spray bottle (warm water helps it to dissolve faster) then spray it on the grout. I also have dark brown colored grout in the shower basin that collected streaks of black mold.

I left the Oxyclean on for several minutes, then used a soft scrubber sponge (the non-scratch kind). The mold completely disappeared.

FYI...I used it to clean all of our wooden decks and outdoor furniture once a year. It cleans all of the mold off of them, I follow up with a light powerwashing or strong hosing off, then re-seal. We live in the PNW so we have to deal with a severe mold buildup from the decks being we most of the year. It works without harming the wood. Same for grout.

Take out bad grout. Put in good grout.

I have used a toothbrush (old one preferably lol) and used Denture toothpaste before. Works a treat.

I keep an old toothbrush in the bathroom so whenever I notice any mold I apply a dab of antiplaque and whitening toothpaste and brush the spot. It's fast and works every time.

I read the previous posts recommending Tilex for mold and mildew on bathroom shower tile... I used it and it worked miracles on my grout and caulk and tiles. I was planning to regrout and now i don't have to!!!!Love this site!

I use X-14 (I wonder if the previous poster meant x-14 and not k-14) and it's only thing that I have found that really works. The house we're renting right now while we build has a major problem and I think they have just caulked over it in the past so it's deep in there. Yuck. I really deep cleaned yesterday and sprayed the x-14 in the corners and within minutes it was gone. It is strong stuff so you do have to watch clothes and towels and open some windows. I'm sure it's horrible stuff but sometimes you just need to use it!!!

We had our main bathroom remodeled in 2005. I know the grout (light gray) was sealed because I did it myself. Then Goth teenager spilled black nailpolish on the floor. She tried to wipe it up but it smeared into the grout lines. I went over it with nail polish remover pads (50 cents each). Let that dry thoroughly then went over it with white latex pain mixed with water. Literally "repainted". It looked okay for several years. But sometime soon I'm going to repeat the paint process.

I would suggest you to clean your grouts with the solution of oxygen bleach and water. This will help in removing molds from your grout lines

Zep Mold and Mildew Cleaner sold at Home Depot was the only product I have used that kept the mold from returning. I used in on the drywall above the shower. It claims to destroy the roots and apparently does since it doesn't pop back up after a short time.