Rosacea occurs primarily on the face and then slowly spreads to other parts of the face or body. Therefore, it is possible to get rosacea on areas other than your face, but that would be usually the neck and perhaps even the back and chest. If it is possible to get rosacea on your arms, it would be incredibly unusual. Keratosis pilaris might be the more likely culprit, since keratosis pilaris usually affects the arms. (Keratosis pilaris is a very common skin condition in which keratin protein forms hard plugs within hair follicles). Keratosis pilaris can get red, dry and irritated (usually from scratching it), it is commonly misdiagnosed as rosacea on the face. However, the biggest visual difference between keratosis pilaris and rosacea is that keratosis pilaris normally appears as the raised "pimples" that gives the look of "chicken skin." As well keratosis pilaris usually does not stay red all the time like rosacea. Another possibility is eczema
that can crop up anywhere, and one of the common areas is top of the arms. Eczema also goes misdiagnosed quite commonly as rosacea. There are other possible skin conditions so I recommend that you visit a dermatologist
who can tell you what kind of skin conditions you have had on your arms.