When You Give Yourself a Disease

Auto-inoculation, or self-inoculation, occurs when a person transfers a disease from one part of their body to another. Self-inoculation frequently happens when someone scratches or rubs a sore and then touches uninfected skin. Many diseases can be spread by self-inoculation in this way, including chicken pox.

In these cases, self-inoculation may be similar to transmission by fomites. For example, imagine that a person ends up with HPV under their nails. In such a circumstance could transmit it either to a partner (fomite transmission) or themselves (self-inoculating). This can happen not just with STDs but other contagious skin conditions, like plantar warts. That is why, in general, doctors encourage people to avoid rubbing sores and warts. They may even recommend covering these lesions to reduce the risk of contact. (Scratching sores can also lead to secondary infections. Those may be even more difficult to heal than the original condition. They occur when a secondary bacteria infects an open sore or wound.)

Soapy hands at sink
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Examples of STDs Where Auto-Inoculation May Be an Issue

Molluscum contagiosum is very easy to spread by self-inoculation. Rubbing a sore can auto-inoculate viral particles to the surrounding skin and lead to additional areas of infection. This is one of the reasons why molluscum contagiosum is so difficult to cure. People often repeatedly spread it to different (or neighboring) body parts by mistake. Molluscum is also an STD where secondary infections can be a big problem if the sores are scratched.

HPV is also known to spread through autoinoculation. In fact, warts on the hands can potentially spread to the genitals. This is true even when those warts are caused by types of HPV not normally associated with genital warts. HPV can also be self-inoculated from the genitals to the mouth. That's why doctors encourage you not to touch or pick at warts.

It is possible for the herpes simplex virus to spread by autoinoculation. There has not been much research on how common this might be. It is conceivable that self-inoculation from mouth to genitals might be possible, although there are no clear reports. Transmission from one partner's mouth to the other partner's genitals is a much more significant risk

How to Reduce the Risk of Self-Inoculation

There are several things you can do to reduce the risk of self-inoculation

  1. Wash your hands frequently, particularly after touching an infected area of your body or the body of someone else who has a skin infection
  2. Do not pick or scratch at sores
  3. Keep sores covered, if necessary, to avoid irritating them or having them rub against other areas of skin
  4. If all else fails, see if your sores or warts can be removed by a doctor. This isn't a cure of the underlying infection. However, it might help if you can't stop yourself from picking at them and extending your infection.
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By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.