How are flat warts caused?

Flat warts are primarily caused by infection with human papillomavirus (HPV), particularly HPV types 3 and 5, which are the main causative viruses. The main causes of the disease include: 1. **Viral infection**: Direct contact with the skin or mucous membranes of an infected person, or indirect contact with virus-contaminated objects such as towels or bath linens, may lead to HPV infection and subsequent development of flat warts. 2. **Weakened immunity**: Individuals with reduced immune function, such as those suffering from certain diseases, experiencing prolonged fatigue, or sustaining injuries, are more susceptible to HPV infection and disease onset. 3. **Skin damage**: Minor skin injuries can also provide entry points for HPV viruses, increasing the risk of infection.