A 1.5 cm hard lump in the back at the ribs is usually caused by sebaceous cysts, lipomas, muscle strains, etc. Sebaceous cysts are usually not serious, lipomas are usually not serious, and muscle strains are also not serious in most cases. 1. Sebaceous cysts: Sebaceous cysts may be triggered by sebaceous gland duct obstruction, skin injury, etc. They are a kind of benign skin tumors, which are generally not serious. Patients may have symptoms such as redness, swelling and bruising of the skin, and they may also have the symptom of hard lumps at the ribs in the back. 2. Lipoma: Lipoma is usually caused by heredity, abnormal fat metabolism and other factors, it is a kind of benign soft tissue tumor, if the volume is small and no discomfort symptoms, it is usually not serious, patients may have symptoms such as localized lumps and hard lumps at the ribs in the back. 3. Muscle strain: muscle strain is usually caused by excessive traction or sharp contraction of muscles in sports, patients may have local redness, swelling and pain, and most of the cases will not cause serious dysfunction, which is not serious. It is recommended that patients seek timely medical attention, identify the cause of the disease under the guidance of the doctor, standardized treatment.