Would like  some effective tips .    

Always difficult to clean when the inside of your gets all sweaty and dirty. That is why on my last helmet I made sure that all the padding and lining was removable and washable.

In the past if my helmet got a sweat sink to it I would let it dry out and then spray with Febreze to eliminate the smell and didn't worry about the appearance.

I imagine you could try a spray upholstery cleaner.

Most of todays new helmets have removable linings,my wife and I both wear modular helmets (Nolan 104 ) all year and sweaty head can really be a problem but the linings are easily removed along with cheek pads and padded neck collar,we wash ours monthly with a few bath towels and our favorite hair shampoo, we found most laundry soaps tend too burn our eyes when closing the shield and we begin to sweat,only did that once Lol. most manufacture's sell replacement linings as well.

Geeesh!!! No wonder my head stinks.

Oh No!!! I feel a Helmet beatn coming on.

Mine all have removable liners, but a quick spray with either Febreeze or a baking soda/water solution in between washes works great. I change helmets every 5-7 years at the most anyway.

When I wear mine, I put on a liner. In hot weather a thin one otherwise a thicker one or a balaclava. It helps to extend the time between cleanings for me. Lots of helmet liners avail I bought some from Zan headgear. I keep a thin one in a pocket of my jacket & one in my vest.

Warm water, a little dish detergent and a sponge, don't soak the liner
but most of my riding is in northern climes and maybe I don't know squat

FF helmet here,the liner snaps out and is hand washable.
Use a little bit of soap n small bucket,dry out in the sun or use a blow dryer.

I use a Shuberth FF. The lining comes out is pieces and I run it thru the washing machine.

My first one was not a removable liner but my accident and smacking my head on the curb it never got stinky. My second one was a loaner and it had a removable liner (like my current one). I looked up on web site of the manufacturer and they recommended washing it and letting it dry outside or if it is above 80 degrees to let them dry inside to prevent shrinking or foam deforming due to very hot air. Here in the south I wash mine every year after the toy ride in december to keep the sweat and dirt from caking up on the liner insert cloth. But when living in such a warm and humidity here in the south I want to keep mold out as long as I can before I get a new helmet.