1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of unit length is a line segment of length 1. In conventions of sign where zero is considered neither positive nor negative, 1 is the first and smallest positive integer. It is also sometimes considered the first of the infinite sequence of natural numbers, followed by 2, although by other definitions 1 is the second natural number, following 0. The fundamental mathematical property of 1 is to be a multiplicative identity, meaning that any number multiplied by 1 equals the same number. Most if not all properties of 1 can be deduced from this. In advanced mathematics, a multiplicative identity is often denoted 1, even if it is not a number. 1 is by convention not considered a prime number; this was not universally accepted until the mid-20th century. Additionally, 1 is the smallest possible difference between two distinct natural numbers. The unique mathematical properties of the number have led to its unique uses in other fields, ranging from science to sports. It commonly denotes the first, leading, or top thing in a group. Etymology
The word one can be used as a noun, an adjective, and a pronoun.It comes from the English word an, which comes from the Proto-Germanic root *ainaz.
Differential diagnosis
It is important to differentiate infantile acne from other forms of acneiform eruptions. Acne venenata infantum is a form of acne characterized by comedone formation and induced by chemical irritants on the skin. This can include comedogenic products such as lotions, ointments, creams and oils. Upon discontinuation of these products, lesions will heal within 6–8 weeks.Other conditions that should be considered include periorificial dermatitis, keratosis pilaris, sebaceous hyperplasia and infections. Pyodermas and panniculitis should be considered in severe cases of inflammatory acne or in cases of acne conglobata while hyperandrogenism should be ruled out in cases of persistent infantile acne. Treatment
Infantile acne is a self-limiting condition that resolves by itself within 6–12 months of occurrence or occasionally by ages 4–5 and does not require treatment in most cases but topical therapies can be used, especially in more severe cases.The goals of treatment are to reduce sebum production, prevent formation of microcomedones, suppress the growth of bacteria and reduce inflammation. As there are no US FDA approved medications for treatment of infantile acne due to lack of high quality trials in patients under 9, recommendations for treatment is based on observations in adult and adolescent populations. Benzoyl peroxide
Benzoyl peroxide (BPO) is first line for mild cases of infantile acne due to its safety and effectiveness. BPO concentrates within cells of sebaceous follicles where it generates free radicals to oxidize proteins in bacteria such as P. acnes. This leads to bacterial death. It additionally works as a mild comedolytic and anti-inflammatory.