ויקרא, פרק י״ג, פסוק כ״ז

The evaluation of skin afflictions is a dynamic process, relying not just on the initial appearance of a mark, but on how it develops over time. When a priest conducts the crucial inspection on the seventh day, he does not need to wait until the day has completely ended. Because a portion of a day is legally considered a full day, the evaluation takes place during the seventh day itself [בכור שור].

During this inspection, if the bright spot has expanded across the skin, the priest declares the individual impure, as the mark is confirmed to be leprosy [ביאור שטיינזלץ]. However, expansion alone does not automatically result in a state of impurity. The newly affected area must still meet the fundamental criteria of the condition, maintaining the required shade of white and appearing deeper than the surrounding skin [העמק דבר]. This principle of expansion applies across multiple stages of the process. Even if the priest had previously cleared the individual and declared them pure, any subsequent spreading of the mark will reverse that decision and render the person impure once again [מלבי״ם, אדרת אליהו].

The specific laws governing afflictions caused by boils and burns share a complete legal equivalence with other types of skin marks. The criteria for impurity and the defining signs are identical across these different conditions, and any mark must meet a minimum size requirement—equivalent to the size of a specific bean—to trigger a state of impurity. However, while the general rules align, there are notable exceptions unique to boils and burns [תורה תמימה, ספרא, מלבי״ם, אדרת אליהו].

In typical skin afflictions, the appearance of healthy flesh within the mark is a sign of impurity. For boils and burns, this rule does not apply. Healthy flesh is only considered a sign of impurity when it is surrounded by natural skin, a condition that cannot be met within a burn scar. Furthermore, if an affliction spreads, the expansion is only significant if it displays the correct color. If the new area is a dull white rather than a distinct leprous shade, it is disregarded and does not cause impurity. Finally, the criteria for these marks are strictly limited to four specific shades of white that appear as deep as an egg membrane. If a mark presents an unlisted appearance, it cannot be classified as leprosy and does not result in impurity.