There isn’t a foolproof way to prevent fungus during active use in a hot, humid environment. The main things that suppress fungal growth are keeping gear dry and limiting conditions that let spores thrive; once you remove those constraints, no chemical shortcut is reliably recommended.

The most practical prevention is still moisture control when the gear is not in your hands: use sealed containers or lens boxes with plenty of fresh, recharged silica gel, and swap/recharge the packs often. Indicating silica gel helps you know when it’s saturated. Rice is sometimes mentioned as a traditional desiccant alternative, but silica gel is the more established approach.

UV/light exposure can also help discourage growth, but it’s not a complete solution during continuous field use.

If fungus is already inside a lens, there is no guaranteed permanent fix short of proper disassembly and thorough cleaning of all affected internal surfaces. Surface cleaning may make it disappear temporarily, but if any residue or spores remain, it can return when humidity rises again. Be cautious with chemicals, as they may damage coatings or lens internals.

In short: you can reduce risk, but not eliminate it in active humid use; and permanent removal usually requires full professional cleaning.