Lemon water moves through the digestive tract, not directly into pigment cells in the skin. After absorption, ascorbic acid is diluted in blood, tightly regulated by homeostasis, and quickly cleared by metabolic pathways. Only a limited fraction reaches the epidermis, far below the concentrations used in dermatology-grade depigmenting agents that can influence melanin synthesis.
Topical lemon juice is a very different exposure. It delivers a low pH mix of citric acid and ascorbic acid directly onto the stratum corneum, stripping lipids, loosening corneocyte cohesion and weakening the skin barrier. Instead of controlled inhibition of tyrosinase, this barrier disruption provokes inflammation, erythema and post-inflammatory hyperpigmentation, which can leave darker, more uneven patches rather than a lighter tone.
Another risk comes from photosensitivity. Compounds in citrus peel and juice, including furocoumarins, can interact with ultraviolet radiation and trigger phytophotodermatitis, a reaction that combines chemical irritation with UV-induced DNA damage. The visible outcome can be burning, blistering and later hyperpigmented streaks or spots that are far more persistent than any fleeting surface brightening effect.
