For example an expense might 1) reduce a company's assets such as Cash, Prepaid Expenses, or Inventory, 2) increase the credit balance in a contra-asset account such as Allowance for Doubtful Accounts or Accumulated Depreciation, 3) increase the balance in the liability account Accounts Payable, or increase the amount of accrued expenses payable such as Wages Payable, Interest Payable, and so on.
In addition to the change in the assets or liabilities, an expense will reduce the credit balance in the Owner Capital account of a sole proprietorship, or will reduce the credit balance in the Retained Earnings account of a corporation.