Leviticus 15:8
And if he that hath the issue spit upon him that is clean; then he shall wash his clothes, and bathe himself in water, and be unclean until the even. And if he that hath the issue spit upon him that is clean; then he shall wash his clothes, and bathe himself in water, and be unclean until the even.
The verse belongs to the hygiene laws that treated contact with bodily discharges as a source of temporary uncleanness and required washing and laundering. If a person with the issue spat on a clean person, that person became ceremonially unclean until evening and had to wash his clothes and bathe himself in water. Contact with an unsafe, contaminated place likewise required washing clothes and remaining unclean until evening.
The rules treated contact with contagious or contaminating conditions as requiring thorough cleansing. The uncleanness kept personal impurities out of the camp, requiring the unclean person to remain outside the camp until evening and to wash himself and his clothing before returning. The regulations served as sanitary measures as well as religious requirements. The same concern for cleanliness applies today, since neglect can spread disease, while removing filth from homes and yards helps protect health.