Hi, Unexplained bruising once in while is understandable but if occurs frequently should be investigated thoroughly since it can indicate an underlying medical condition or ailment Many times taking medications like aspirin, ibuprofen, non steroidal anti-inflammatory drugs increases chances of sudden bruising. Topical and systemic corticosteroids cause skin thinning, making one prone to bruises. Many a time bruising can be caused due to liver ailments, kidney diseases and blood disorder. I do hope that you have found something helpful and I will be glad to answer any further query.