Help with spots on old negatives

[ismael]

Hi,

I'm getting some experience scanning older negatives. I have an antistatic brush for loose dust and PEC-12 emulsion cleaner.
However, some negatives have this problem: Yellow spots, especially in lighter colors like sky or walls. These are not that old. Maybe 15 years or so. But improper storing combined with our tropical heat and humidity may have something to do with this.

The brown area in the left is caused by curling of the negative as it was cut right on the image. But that's another story.
I suspected fungal damage but I don't percieve any roughness on either side.

TEST RESULTS:

I did a test with this one, which is roughly the same age: (My young sister's teddy bear with my hat, my sunglasses, my watch and my pilot's headset. I was flattered )

Scanned untouched:

Scanned after cleaned with PEC-12 and a water wash with a few drops of mild dish detergent. Disregard the white balance as this was a quick test.

The only gain was dust improvement. I don't see any degradation either so that's a good thing.

Any idea what is it or how to deal with it?

I'll keep experimenting with this. I'm constantly finding more and more negatives.
Just for the record I'm using an older Epson 2400 scanner and Vuescan. Looking to eventually upgrade to a higher resolution scanner or maybe a dedicated film scanner.


Thanks,