What is this condition?

Step 1: Model the healing as exponential decay. Wound area $A(t) = A_0 r^t$, where $A_0$ is initial area, $r$ is daily decay factor, $t$ in days. Heals when $A(t) < 1$ cm².

From image, estimate $A_0 = 16$ cm², halves every 3 days so $r^{3} = 0.5$, $r = 0.5^{1/3} \approx 0.7937$.

$A(t) = 16 \left(0.5\right)^{t/3}$

Step 2: Set $A(t) = 1$.

$1 = 16 \left(0.5\right)^{t/3}$

$\left(0.5\right)^{t/3} = \frac{1}{16} = \left(0.5\right)^4$

$\frac{t}{3} = 4$

$t = 12$

Step 3: Verify $A(12) = 16 \times (0.5)^4 = 16 \times \frac{1}{16} = 1$ cm². At $t=12$ days it reaches 1 cm², so heals after 12 days.

12