Nitric Acid nitrates the amino acids, as well as dissolving minerals, which then allows it to remove layers of soil and not be stopped by 'bio-layering' which can occur when multiple brews are done without performing a cleaning regimen between each brew.
Nitric acid vapor is a strong irritant at lower concentrations and can cause conjunctivitis and even necrosis of the conjunctiva. Dermal exposures: Nitric acid is corrosive to the skin, producing severe burns, ulceration, scarring, dermatitis and yellow staining of the skin.
Toxicity after inhalation exposure to nitric acid is similar in humans and animals. Nitric acid fumes may cause immediate irritation of the respiratory tract, pain, and dyspnea, followed by a period of recovery that may last several weeks.