A critical factor that plays a part in susceptibility to colds is age. A study done by the University of Michigan School of Public Health revealed particulars that seem to hold true for the general population. Infants are the most cold ridden group, averaging more than six colds in their first years. Boys have more colds than girls up to age three. After the age of three, girls are more susceptible than boys, and teenage girls average three colds a year to boys' two. The general incidence of colds continues to decline into maturity. Elderly people who are in good health have as few as one or two colds annually. One exception is found among people in their twenties, especially women, who show a rise in cold infections, because people in this age group are most likely to have young children. Adults who delay having children until their thirties and forties experience the same sudden increase in cold infections. The study also found that economics plays an important role. As income increases, the frequency at which colds are reported in the family decreases. Families with the lowest income suffer about a third more colds than families at the upper end. Lower income generally forces people to live in more cramped quarters than those typically occupied by wealthier people, and crowding increases the opportunities for the cold virus to travel from person to person. Low income may also adversely influence diet. The degree to which poor nutrition affects susceptibility to colds is not yet clearly established, but an inadequate diet is suspected of lowering resistance generally.

    年齡是人們是否易患感冒的一個重要因素。 密歇根大學(xué)公共衛(wèi)生學(xué)院揭示了一些對人們普遍適用的細(xì)節(jié)。 嬰兒期是最易感冒的時期，從出生到一周歲平均感冒六次。 在三周歲前，男孩比女孩感冒次數(shù)要多。 但三周歲后，女孩就更易感冒了。 十幾歲的女孩年平均感冒三次，男孩則為兩次。 一般說來，隨著年齡的增長，感冒的次數(shù)也越來越少。 健康的老年人每年只感冒一至兩次或更少。 但在二十至三十歲之間的人尤其是婦女出現(xiàn)了例外。 他們感冒的次數(shù)有所增加，其原因在于人們通常在這一時期帶養(yǎng)小孩。 那些晚育至三十幾歲或四十幾歲才有孩子的人，在那一時期感冒次數(shù)也會突然增加。 研究還發(fā)現(xiàn)，經(jīng)濟(jì)狀況與感冒息息相關(guān)。 隨著收入的增加，家庭成員的感冒次數(shù)呈下降趨勢。 家境貧寒的人感冒次數(shù)要比最富裕的人多三分之一。 低收入者被迫擠住在比富人居所狹小得多的空間里。 擁擠的狀況為感冒病菌的傳播提供了條件。 低收入同樣不利于合理的飲食結(jié)構(gòu)。 營養(yǎng)不良到底對患感冒造成多大的影響目前尚不清楚，但不合理的飲食通常降低了人體的抵抗力。