ויקרא, פרק י״ג, פסוק ל״א

Diagnosing an affliction on the scalp or beard requires the priest to carefully evaluate signs of purity and impurity. In cases of uncertainty, the Torah mandates a period of isolation and observation. When examining these conditions, which typically involve hair loss, certain rules mirror those of standard skin diseases. For instance, the affected area must be at least the size of a bean to be deemed impure, and the affliction does not spread inward upon itself [תורה תמימה, מלבי״ם, אדרת אליהו]. However, unlike other skin diseases that must appear white, a scalp affliction is considered impure regardless of its color and is not restricted to the four standard shades of skin ailments [ביאור יש״ר].

The primary factor that determines whether a person must be quarantined is the absence of dark hair within the affected area. From this requirement, commentators deduce that if healthy hair were present, the individual would be declared completely pure and exempt from isolation. In standard skin diseases, hair that changes color signals impurity. In contrast, when dealing with a scalp affliction, new hair growth is a clear indicator of healing and recovery [רש״י, רשב״ם, רלב״ג, הופמן]. This distinction is emphasized so that one does not mistakenly view healthy hair growth as an ongoing sign of illness or a reason for further quarantine; rather, its presence immediately establishes purity [מזרחי, שפתי חכמים].

Although black hair is specified as the sign of healing, this is merely an example representing the most common and natural hair color [שטיינזלץ, מלבי״ם, אילת השחר]. In practice, any hair color, such as red or green, serves as a sign of purity. The only exception is thin, yellow hair, which is the definitive mark of impurity for scalp ailments [תורה תמימה, אדרת אליהו, הירש]. To qualify as a sign of healing, there must be at least two hairs of sufficient length [רלב״ג, הירש, הופמן]. Furthermore, these hairs must be fully enclosed within the affliction. It is insufficient for hair to grow at the edges where the disease never reached; the ailment must surround the hair completely, proving that the growth occurred directly within the affected zone [תורה תמימה, מלבי״ם, אדרת אליהו].

When an affliction lacks the definitive signs of impurity, such as depth or yellow hair, but also lacks the clear sign of healing indicated by healthy hair growth, the priest cannot make an immediate ruling. As a result, the individual must be placed in quarantine for seven days. While this procedure is standard for unresolved cases, there is a disagreement among the sages regarding the exact criteria for isolation. Some maintain that multiple conditions must be present simultaneously to require quarantine, while others argue that the absence of even a single clear sign is enough to mandate the waiting period [דעת זקנים].