reactive

reactive — adjective

1. describing a person, team, or system that deals with problems only after they ha

1.adjectiveB2
Definition

describing a person, team, or system that deals with problems only after they happen, rather than taking action beforehand to prevent them.

Example

Talia's team took a reactive approach, fixing bugs only after customers reported them.

reactive approach — common collocation in management writing

Rafael warned the board that a purely reactive strategy would leave them trailing behind competitors.

Common collocations
  • reactive approach
  • reactive strategy
  • reactive response
  • reactive management
  • purely reactive
  • less reactive
Synonyms
  • passive

    stronger implication of inaction; reactive at least responds, passive may do nothing

  • defensive

    narrower scope — focuses on warding off threats rather than responding to any event

  • responsive

    positive connotation of quick helpful reaction; reactive often carries a negative sense of being too late

Antonyms
  • proactive

    acting in advance to prevent or shape events rather than reacting to them

Grammar Patterns

reactive + noun

be + reactive

Usage Note

Frequently contrasted with proactive in business and management writing. The subject is typically an approach, strategy, team, or organizational culture — not an individual's personality trait.

Common Mistakes

We need a proactive team that only fixes problems after they appear.
We need a proactive team that prevents problems before they appear.
'proactive' means acting in advance; 'reactive' means responding after the fact. Learners often confuse the pair.

2. describing a substance that easily undergoes chemical change when it comes into

2.adjectiveB2
Definition

describing a substance that easily undergoes chemical change when it comes into contact with another material.

Example

Rin's chemistry teacher explained that sodium is highly reactive and must be kept under oil.

highly reactive — adverb + adjective intensifier pattern

Saira checked the data sheet to find which reactive compounds were in the mixture.

Common collocations
  • highly reactive
  • chemically reactive
  • reactive metal
  • reactive compound
  • reactive element
  • reactive gas
Synonyms
  • unstable

    broader term covering both chemical and physical instability; reactive is specifically about tendency to change chemically

  • volatile

    implies evaporation or explosive risk; reactive covers any chemical change including mild ones

  • active

    vaguer term; reactive is more precise in chemistry contexts

Antonyms
  • inert

    describes substances that do not readily undergo chemical change, such as noble gases

  • stable

    describes substances that resist chemical change under normal conditions

Grammar Patterns

be + reactive

highly reactive + noun

reactive + noun

Usage Note

Common in laboratory and industrial safety contexts. Elements near the top of the reactivity series (e.g. alkali metals, halogens) are typically described as highly reactive. Often appears in warnings and handling instructions.

Common Mistakes

Lithium is a reactive reaction.
Lithium is a reactive element.
'reactive reaction' is redundant; the quality of being reactive already implies a tendency to react.

3. describing a living organism, organ, or tissue that quickly responds to sensory

3.adjectiveC1
Definition

describing a living organism, organ, or tissue that quickly responds to sensory input such as touch, light, sound, or chemical contact from its surroundings.

Example

Ayana noticed that her skin was unusually reactive to the ingredients in the new lotion.

reactive to [substance] — preposition pattern for stimuli

The doctor shone a light into Dahlia's eyes and confirmed that both pupils were reactive.

pupils were reactive — fixed medical expression

Common collocations
  • reactive to light
  • reactive to touch
  • reactive skin
  • reactive pupils
  • highly reactive immune system
Synonyms
  • responsive

    more general term; reactive in medicine implies an observable physical response to a specific stimulus

  • sensitive

    overlaps in meaning but broader — can include emotional sensitivity; reactive is physical only

Antonyms
  • unresponsive

    medical term for tissue or organ that does not respond to stimuli

Grammar Patterns

reactive to + noun

Usage Note

Primarily used in medical examinations and biological descriptions. Pupil reactivity and skin reactivity are the most common clinical contexts. Distinguish from sense 2: this sense applies to living tissue responding to stimuli, not to chemical substances reacting with each other.

Common Mistakes

The patient's skin is reactive to sunlight — it must be stored in a cool place.
The patient's skin is reactive to sunlight
she must avoid prolonged exposure.' — 'stored' is used for objects and substances (sense 2), not for living tissue (sense 3).

Word family

Synonym discussion

Sense: adjective/1

These four words all describe ways of dealing with events, but differ in timing and attitude. Reactive means responding after something happens, often with a slightly negative tone of being too late. Passive goes further — it implies accepting whatever happens without any response at all, which makes it more extreme. Defensive is narrower: it specifically describes actions taken to protect against a perceived threat, rather than any kind of event. Responsive is the most positive of the group; it suggests a quick and helpful reaction, whereas reactive often implies that the reaction was forced by circumstances. For example, a fire department that arrives in two minutes is responsive, not reactive. A company that only adds security features after a hack is reactive, not defensive.

reactive ↗passive ↗defensive ↗responsive ↗

Common collocations

Nouns

Adverbs

Phrases

  • reactive approach to
  • reactive to light
  • reactive to stimuli

Prepositions

Etymology

LatinFrenchEnglish

Reactive is formed from react (to act back) plus the adjective suffix -ive (having the quality of). The word react traces back through Latin re- (back, again) and agere (to do, drive, act), passing through French and into English. The chemical sense emerged in the mid-1800s alongside the growth of laboratory chemistry, and the management/behaviour sense followed in the 1900s as the word broadened from science into everyday use.