Adults in America frequently have asthma. Although there was little research on the long-term trajectory of asthma in American adults, the prevalence of asthma has changed throughout time. For a study, researchers sought to examine the risk factors for asthma and detail the prevalence and trend of asthma in American adults from 2005 to 2018. From 2005 to 2018, the National Health and Nutrition Examination Survey was used to collect data. The weighted and unweighted percentages of healthy participants, asthma patients, and asthma trends were computed. The risk variables for asthma were examined using weighted univariate logistic regression. The study included 39,601 adult participants in total. Between 2005 and 2018, 8.41% of adult Americans in America had asthma, compared to 8.30%, 8.70%, and 7.92% for young, middle-aged, and elderly individuals. The estimated prevalence of asthma in middle-aged and elderly adults was stable over time (P for trend=.33, difference=0.015 and P for trend=.80, difference=-0.024, respectively), while it increased over time in young adults and adults overall (P for trend=.03, difference=0.023 and P for trend=.007, difference=0.060, respectively). Adults in America had an increase in asthma. An increased risk of having asthma was connected with female sex, non-Hispanic Blacks, poor yearly household income, active smokers, obese patients, patients with hypertension, diabetes, and people with a family history of asthma.