Microdermabrasion is another mechanical method of exfoliation. Skin care is often provided up to the knee, including granular exfoliation, moisturizing, and massage. Skin exfoliation causes the henna tattoo to fade. Limiting time in the shower and using gentle exfoliation to unplug pores can help. Ingrown hairs are also caused because of lack of natural exfoliation in the skin. Bringing a shave brush across one's skin produces a mild exfoliation. Human skin is also subjected to abrasion in the form of exfoliation. This type of exfoliation is recommended for people treating acne. The constant thickness of the cornified layer results most commonly from regular superficial exfoliation. Achieving single layers typically requires multiple exfoliation steps. After exfoliation the flakes are deposited on a silicon wafer. The synthesis of phosphorene mainly consists of micromechanical cleavage or liquid phase exfoliation methods. Graphite fluoride is a precursor for preparation of graphene fluoride by a liquid phase exfoliation. It is directly implicated in epithelial cell damage, exfoliation, and bronchospasm in allergic diseases. In the last case mechanical exfoliation of hydrogenated top layers can be used.