Anyone who has spent an afternoon at the bandsaw with cocobolo knows what the wood charges for the privilege. Blotchy forearms by dinner. A nose that runs for two days. The rosewoods do it too, some people worse than others, and most shops learn which boards mean gloves and a respirator the same way they learn everything else. The hard way, once.
Here's the part almost nobody connects. That rash is a finishing forecast.
The same compounds in cocobolo and the rosewoods that light up your skin are the ones that stall an oil finish. It's one family of molecule doing two jobs. It grabs onto proteins in your skin, and your immune system files a complaint you feel for a week. And it grabs the chemistry an oil finish needs to harden, the same chain reaction that gives teak its oil trouble, and holds it down the same way. Same grabby molecule, two targets. The wood that gets under your skin is the wood that will leave your oil finish tacky for a month.
Which hands you a shortcut for exactly the situation where you have no other data. Exotics are the woods you're least likely to have finished before. You've got one gorgeous offcut of something unfamiliar, you want oil to bring up the figure, and the usual way you find out whether the oil will cure is by ruining the offcut. There's a faster read, and you already carry it: the wood's reputation. If a species is famous for making people itch, treat it as oil-incompatible until a test board proves otherwise.
And the reputation travels by family, not just by species. The reason someone who reacts to one rosewood reacts to all of them is that the compounds across the whole genus are built on the same skeleton. The structural kinship that makes the allergy travel is the same kinship that makes the finishing problem travel. One bad afternoon with cocobolo is telling you about every rosewood on the rack.
Two refinements before you act on this. First, the rosewoods are a worse bet for oil than teak, not a better one. Their particular poison is more aggressive at killing a cure than teak's, so if you've gotten away with oiling teak once or twice, don't let that make you brave. Second, if you go the degrease-and-finish route, the wipe-with-solvent-then-oil-fast trick that works on teak, know that the window is tighter. Rosewood oils creep back to a cleaned surface faster than teak's do. Where teak gives you half an hour, figure fifteen or twenty minutes. Solvent wipe, let it flash, oil on. Don't break for coffee.
The fallback is the same as for teak: shellac. It cures by chemistry the extractives can't touch, and it goes hard over cocobolo the same as it goes hard over pine. If the figure is what you're after, shellac will show it to you, and you can build whatever you want on top.
One honesty note, because this is a rule of thumb and not a law of physics. The rash-to-finish read is mechanism-backed and it will steer you right far more often than not, but it's a probability, not a verdict. The test board is still the final word. The shortcut just tells you which woods have earned one before you commit the good stock.
So the next time a board makes your forearms itch, write that down twice. Once for the gloves. Once for the finish schedule.