There are a variety of Evening Primrose species, but the oil is usually from Oenothera biennis seeds. The oil is very high in linoleic acid (about 70%) and γ-linolenic acid (about 10%) with other fatty acids including: palmitic, oleic, stearic, and myristic acids. It also has flavonoids, proteins, vitamins and minerals. These make this oil very good at dampening inflammation in skin and preventing it from spreading. This has been demonstrated in studies on atopic dermatitis and psoriasis.
As with Evening Primrose oil, Rosehip oil can be made from a variety of species, Rosa canina is the best studied and the most likely to be used in Europe, or Rosa rubiginosa. This contains almost equal amounts of linoleic acid (42%) and a-Linolenic acid (38%), Oleic acid 12% , palmitic acid (5%) and a few others. The most abundant vitamins are C, A and E which can all be very beneficial to skin function and healing. The tannins make it feel astringent, but it has been shown to benefit dry skin and maintain softness in the skin. The flavonoids help with antioxidant potential.
However, for extremely sensitive skin, I would approach with caution as both (in fact most botanical extracts) can cause allergic reactions. If your skin is very sensitive, perhaps you could start using shea or mango butter with a little jojoba or almond oil oil mixed in to see how your skin reacts, the butters will also be beneficial for your dry skin. If you don’t react to either, then you may want to try these two oils, one at a time, again mixed with the butters. Their fatty-acids profiles, above, gives you some sense of what they might be expected to help. The Evening Primrose is possibly a more comprehensive anti-inflammatory and Rosehip offers antioxidant properties and a nice high vitamin C content, so should help to restore depleted skin and offer some protection from UV damage and pollutants.
For dehydrated skin you can add hyaluronic acid mixed in glycerine or sorbitol, add to the oils and butters above (you will need to use an emulsifier if you are making this yourself) or you can apply the glycerine and hyaluronic acid to damp skin. I always recommend using a good hydrosol for cleansing and toning in one. This leaves even sensitive skin well hydrated and provides enough oil to improve very dry skin. After this, you can apply the butters with the oil or just the oils.
Both vitamin A and C from Rosehip, should be helpful in the mid to long-term strengthening of the skin. But until the dehydration is rectified, and you have determined what improves and what worsens your sensitive skin, I wouldn’t experiment too wildly. When your skin is well hydrated it will function much better and you will then get far more out of any fatty-acids, vitamins and minerals you put on it.