Dry syndrome can be divided into two types: primary and secondary. When only dry syndrome occurs without the presence of other autoimmune diseases, it is called primary dry syndrome. And if dry syndrome exists together with other connective tissue diseases, it is called secondary dry syndrome. Incidence According to the literature, the incidence of secondary dry syndrome ranges from 4% to 31%, and this difference is based on the different diagnostic criteria used. The incidence of secondary dry syndrome also varies in different connective tissue diseases. In rheumatoid arthritis the incidence ranges from 4% to 31%, in patients with systemic lupus erythematosus from 8% to 19%, and in systemic sclerosis from 14% to 29%. Difference from primary dry syndrome? Although secondary dry syndrome is common, there are not many studies about this disease. In addition, there is no definite conclusion about whether secondary dry syndrome is a manifestation of the underlying disease or an overlap between primary dry syndrome and other diseases. However, some studies have found that patients with desiccation syndrome secondary to SLE are younger compared to primary desiccation syndrome, but are similar in terms of clinical symptoms, serologic features and glandular pathology biopsy, differing only in the degree of perivascular lymphocytic infiltration seen on salivary gland biopsy. There are also studies showing that patients with dry eye and dry mouth symptoms can occur in both primary and secondary systemic sclerosis, and the positive rate of autoantibodies and histopathological examination are also similar, further suggesting a common pathogenesis between the two. However, patients with desiccation syndrome secondary to rheumatoid arthritis have atypical clinical symptoms and the incidence of salivary gland swelling is much lower. In a recent study, although symptoms of dry mouth and dry eyes and related antibodies can also occur in secondary dry syndrome, the incidence of clinical symptoms and the positive rate of anti-Ro antibodies are higher in primary dry syndrome. Lip gland biopsy suggests that lymphocyte infiltration in primary desiccation syndrome is mainly B cells.