Final answer:
Susie should modify her sun exposure and apply sun protection to address the difficulties in tanning her legs and maintaining color. Understanding that melanin synthesis peaks around 10 days after initial sun exposure and that tanning is an impermanent process can help her manage her tanning routine safely.
Step-by-step explanation:
Susie, who has skin type 3 and is experiencing difficulty tanning her legs and maintaining her tan color, may need to revise her tanning approach. It's important to know tanning impermanence occurs because melanosomes, which contain melanin, are temporary structures destroyed by fusion with lysosomes. Furthermore, the melanin-filled keratinocytes in the stratum corneum will slough off, continuously altering the tan's appearance.
To address her concerns, Susie should consider modifying her sun exposure, ensuring she doesn't tan too frequently, as it takes about 10 days after initial sun exposure for melanin synthesis to peak. Moreover, Susie should use sun protection, such as sunblock or sunscreen with an appropriate SPF rating, to prevent overexposure to UV radiation, which can increase the risk of skin cancer. Applying these protective measures and understanding the tanning process may help her achieve a more even and lasting tan, especially on harder-to-tan areas like the legs.