Healthy individuals, those with health levels above the “optimal” level, may desire to substitute health capital for more liquid capital. In other words, individuals may wish to “sell” their health. But, as Eq. (4) shows individuals cannot “choose” health optimally. Instead they can consume medical care (medical health investment) I(t) optimally. But medical care I(t), viewed as healthpromoting cannot be traded (individuals cannot “sell” health through negative medical health investment) and is therefore positive for all ages I(t) ≥ 0. As a result health cannot deteriorate faster than the health deterioration rate d(t). This corresponds to the corner solution I(t) = 0.