Definitions of irritate:

• verb:   excite to some characteristic action or condition, such as motion, contraction, or nervous impulse, by the application of a stimulus

  Example: "Irritate the glands of a leaf"

• verb:   excite to an abnormal condition, of chafe or inflame

  Example: "Aspirin irritates my stomach"

• verb:   cause annoyance in; disturb, especially by minor irritations

  Example: "It irritates me that she never closes the door after she leaves"