There are two ways this question can be meant:
1: Can you use the same set of brushes in both your oil and acrylic paintings rather than having separate sets?
2: Are there types of brushes that should be used only with oil or acrylic?
I put a piece of masking tape around the end of the handles of the brushes I use for oil paint so I never use them for acrylic. It's means I never have to worry about about cross-contamination. You could be meticulous about cleaning a brush to swap mediums, but would you truly always be...?
Some synthetic hairs don't like the solvents that can be used to thin oil paint and rinse brushes. See what the manufacturer says in their description of the brush in a leaflet or info on the point of sale display. With acrylics, because it's relatively easy to have the paint dry in a brush and ruin it, I don't use expensive sable hair brushes but keep them for watercolor and oil.
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