For cleaning my wonderful Rosemary brushes, I use only soap and water. I use a certain laundry soap which is home made in Romania in the country. Lately I discovered that my brushes can be washed only once a week or so, if I leave them to sit almost horizontally in a tray with artist poppy seed/safflower oil. First I deep the brushes in oil and wipe them with a cloth, then I dipped the hairs in this oil and it works wonders. I read that washing could damage brushes, plus I sure save a lot of time. In the morning I wipe my brushes and they are ready to paint.
The main reason why some artists become sensitive to oil painting, is not because of the paint but because of the toxicity of traditional mediums. Oil paints are relatively non-hazardous in themselves. Unless you eat them or let them come into contact with your skin. Let's see what mediums are out there.
Maimeri produces an eco friendly oil medium. It has the consistency of the water, it has a slight alcohol odor, safe for health and environment, can be discarded in the sink, and it is widely available online. I started using it and I am thrilled about it. Diluting only with oil made the layers of paint thick and kind of sticky. With this medium I can paint very thin transparent layers, plus it helps with very fine details. Using too much of this medium can make the paint look matte, but for superior layers, I mix it with a bit of poppy seeds oil.
Recently I discovered a new vegetable thinner produced by Tintoretto, I tried it, but personally I prefer Maimeri. I read on their website that it has no odor and is not volatile: "Revolutionary vegetable product, both usable as a thinner for oil colours, as well as a solvent for brushes cleaning. Of a new generation, it meets the current safety and environmental protection requirements. Exceptional in its main features: NOT NOXIOUS for man and nature, NOT VOLATILE, ODOURLESS and for the present time turned out to be hypoallergenic. "
Citrus turpentine has a lower odor and a slower evaporation rate than the conventional turpentine, but it's still a neurotoxic.
The spike lavender oil seems fine, at least theoretically, safe enough to use, though it could produce temporary memory loss, and you do need good ventilation in your studio, or you might never want to smell any lavender ever again. The very high price might be though quite inconvenient for most artists. Spike lavender is different from the lavender we know, it grows on the sea side. Many say that Oil of Spike Lavender was the medium used by Leonardo as well as the Netherlands painters, and Rubens used it to enrich his colors. If you consider using it, take into account that it is a very strong solvent, some say that you shouldn't use too much. It is produced by Lefranc and Bourgeois, Holbein, and other brands.
Odourless mediums and solvents are based on fast drying alkyd resins which out perform ‘traditional’ mediums. They evaporate more slowly than turpentine so that less vapor is generated during a painting session. They do, however, evaporate over time, and the problem with odorless solvents is that artists often forget that they are still very toxic. Drying racks as well as work spaces still need to be ventilated and painters in lofts should not recirculate the same studio air in living and sleeping areas because a slow vapor build up could become toxic. I wouldn't recommend to use this medium if you paint in your home or in a shared studio.
Traditional mediums evaporate very fast releasing toxic vapors. Aromatic solvents like gum or mineral turpentine will affect your health with years of regular use because you cannot escape the fumes. Using toxic solvents and mediums in public shared spaces is like passive smoking. Ultimately it is best to avoid these types of solvents.