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The most common causes of lump in the labia are Bartholin's cyst,Nabothian's cyst or sebaceous cyst.Usually these are common and go by themselves.
Avoid wearing tight undergarments.
Wash the area twice with antibacterial soap and water.
Do not squeeze or pull it.
If swelling,pain or pus is there then kindly visit a Gynaecologist as you may require prescription antibiotics.
Take Care!