The first time it became horny to me was as a teenager working delivering rental water softeners. The equipment was almost always in a basement, or a laundry room, and since the route was during business hours the houses were almost always unoccupied.
By accident I noticed a couple of laundry baskets of dirty clothes and saw a pair of panties laying on top. My curiosity got the better of me and I picked them up to find they had been worn. I quickly held them to my nose to find the unmistakable scent of pussy, musky and very horny. I was immediately hard. I had no idea who was in the household, all I knew is they were traditional panties, not bikini style, and a pastel color that smelled wonderful.
My curiosity got the better of me and I dug a little deeper in the basket to find another pair adorned with cartoon characters in a bikini style. I smelled them and discovered a completely different scent, likely a much younger crotch. I did not act on my discoveries by masturbating, but I sure thought about it.
On a second delivery to the same house I saw framed family photos on a kitchen countertop and got a good look at who wore the panties I had found. Mom was very attractive and maybe 40. There were two younger girls in the photo, but it was mom's scent that really got me hard. On a subsequent delivery I again found laundry baskets and located a pair of mom's used panties. They were a dark blue color and had light colored stains in the crotch, suggesting she had been really wet at some point or perhaps leaked cum after having sex. I tasted them mesmerized how horny a stranger's dirty panties made me. I immediately masturbated and shot a huge load onto the crotch of her panties, I couldn't help myself.
It was very horny, and I would occasionally find and enjoy dirty panties in other basements, but I never came on another pair because it seemed risky.