Welcome to HealthcareMagic. Kissing can lead to transmission of viral or fungal diseases which are contagious. If he is free from STD’s then also the chances of transmission of oral herpes( HSV1
) is there. This viral infection is often asymptomatic and cycles between periods of active disease and a remission period. After initial infection, the virus moves to sensory nerves (sacral ganglia), where it becomes latent and reside life-long. So the boy may be having HSV 1
which is transmitted by kissing and may not be knowing about it.
Hope it helps you. Regards.