yeh they're soooo funny aren't they ?
Usually caused by heat so much more common in the summertime or humid conditions. I usually suffer a couple each year in the hot weather but have been fortunate so far this year… I've had them in the past on areas which don't even have contact with the saddle so chaffing and poor fitting saddles aren't always the cause.
For long rides I use hibiscrub (chlorhexidine)- available in boots or any chemists. Apply it to yourself and the chamois of your shorts. I find it seems to work.
For the actual boil itself I've been prescribed fucidin cream in the past. Use it three or four times a day with the chlorhexidine and it should start to go down. Wearing loose fitting clothes helps when not on the bike, always change out of sweaty cycling gear asap and wash straight away. Boils can be squished but be extrememly careful. Make sure hands are washed with hibiscrub and have it ready to clean the area immediately afterwards.
Antibiotics also work but are not really a solution, more of a last minute fix it, tell the doc (if you go) that you have a cycling holiday booked up!
Get it sorted quick though, years ago i ended up having to have one surgically removed, something I never ever want to have to go through again.
Kev