Answer: Wish there were an easy solution! Deer flies are usually active for specific periods of time during the summer. When outside, repellents such as Deet and Off (N-diethyl-meta-toluamide) can provide several hours of protection. Follow label instructions because some people can develop allergies with repeated use, look for age restrictions.
Permethrin-based repellents are for application to clothing only but typically provide a longer period of protection. Repellents can prevent flies from landing or cause them to leave before feeding but the factors that attract them (movement, carbon dioxide, etc.) are still present. These flies will continue to swarm around even after a treatment is applied.
Light colored clothing and protective mesh outdoor wear may be of some value in reducing annoyance from biting flies. In extreme cases, hats with mesh face and neck veils and neckerchiefs may add some protection.
Sorry I don't have more to offer!
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