The basics
‘Affect’ is a verb. It means to influence something, e.g.
Diet affects a person’s risk of cancer.
Diet actively influences a person’s risk of cancer.
‘Effect’ is a noun. It means an outcome, i.e., the result of an action:
An effect of global warming is poorer air quality.
We are describing the result (‘poorer air quality’) of an action (‘global warming’).
‘Affect’ and ‘effect’ are often interchangeable
X has an effect on Y.
X is affected by Y.
These statements have the same meaning.
A quick reminder of verb tenses
Remember, only ‘affect’ is a verb, whereas ‘effect’ is a noun. The following table only applies to ‘affect’. For more information, see our blog Verb tenses in scientific manuscripts.
| Verb tense | When to use | Example |
| Present | Use when stating general truths. | Diet affects a person’s risk of cancer. |
| Present perfect | Use when describing actions that happened in the past but are still relevant today. | In this study, we focus on how the Great Recession has affected the iconic “American Dream.” |
| Past | Use when discussing previous studies or past events. | A quarter of all obese patients were affected by severe sleep apnea. |
| Past perfect | Use when describing an action that occurred before another action. | Telephone interviews were conducted with private households which had been affected by the 2013 floods in Germany. |
| Past continuous | Use when describing an ongoing action that occurred in the past. | It was found that the cutting strategy was affecting the geometry of second-order microstructures. |
| Present continuous | Use when describing events that are happening at the moment of writing. | The purpose of this study was to investigate what factors are affecting job-seeking stress in nursing students. |
| Future | Use when discussing the implications of the study. | Flooding events will affect more people in the future as a result of sea-level rises. |
Quick ways to identify a noun
Remember, ‘effect’, as a noun, will likely be preceded by definite/indefinite articles, e.g., ‘an effect’, ‘its effect’, ‘the effect’ … etc.
Alternative verbs/nouns
You may find it helpful to use an alternative verb/noun to help you decide whether to use ‘affect’ or ‘effect’. If the meaning of the statement is retained using an alternative verb, then ‘affect’ is correct. If the meaning of the statement is retained using an alternative noun, then ‘effect’ is correct.
| Alternative verbs for ‘affect’ | Example |
| Change | Diet changes a person’s risk of cancer. |
| Alter | Diet alters a person’s risk of cancer. |
| Influence | Diet influences a person’s risk of cancer. |
| Alternative verbs for ‘effect’ | Example |
| Result | A result of global warming is poorer air quality. |
| Outcome | An outcome of global warming is poorer air quality. |
| Consequence | A consequence of global warming is poorer air quality. |
Real-world examples from STEM articles
Sleep deprivation negatively affects various cognitive performances.
The effect of resistance exercise on glycemic control in type 1 diabetes is unclear.
In this study, we focused on events of severe water limitation that affect ecosystem structure and functioning.
The potential difference between the model alloys and aluminum was affected by pH value.
We investigated the effects of temperature on thermophilic anaerobic digestion of cattle manure.
Global warming will affect the genetic diversity and uniqueness of Lycaena helle populations.
All cultivars grown were affected at approximately 5 to 35% symptomatic plants per field.
In this study, we examine the factors affecting biomass enzymatic reactivity.
The high molecular weight glutenin subunits were the most affected.
Aspirin has shown a protective effect in population-based studies.
Naturally occurring VHL mutations have been evaluated to determine their effect on HIF-a ubiquitination.
A favorable effect of high intakes of milk and yogurt has been suggested by a hospital-based case-control study.
In addition to its effect on p53 checkpoint function, deletion of p14AR7 also affects the expression of p27.