The recurrence of a sebaceous cyst behind the neck after surgery may be due to incomplete removal of the affected tissue during the operation or postoperative wound infection, among other reasons. In such cases, it is recommended that patients seek medical attention promptly and undergo evaluation and treatment by a professional doctor.

1. Re-examination and Evaluation: First, you need to visit a dermatology or surgery department for a follow-up examination, allowing the doctor to assess the recurrence of the sebaceous cyst, including its size, location, and whether it is accompanied by infection, among other factors.

2. Medical Treatment: If the cyst is in the early stage of recurrence, small in size, and without obvious signs of infection, the doctor may recommend conservative treatment with medications such as antibiotics or anti-inflammatory drugs.

3. Surgical Treatment: If the cyst is large or accompanied by infection, surgery may be necessary again. During the procedure, the doctor will aim to remove the affected tissue as thoroughly as possible to prevent recurrence.

4. Adjuvant Therapies: After surgery, patients should pay attention to wound care to avoid infection. Physical therapies such as warm compresses and massage may be used to promote wound healing.

5. Lifestyle Adjustments: Maintain good lifestyle habits, such as avoiding staying up late for extended periods, boosting immunity, and practicing personal hygiene, to reduce the risk of cyst recurrence.

It is advisable to seek medical attention as soon as possible, so that a professional doctor can formulate an appropriate treatment plan based on your specific condition. At the same time, follow the doctor's recommendations and actively pursue treatment in order to recover at the earliest opportunity.