Hello, Thanks for writing to us. 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. So let me know have you take any drug presently or having any history of injury. I do hope that you have found something helpful and I will be glad to answer any further query.