Organization and Accounting Pronouncements	12 Months Ended
Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Accounting Pronouncements	1. Organization and Accounting Pronouncements Description of Business Equillium, Inc. (the Company) was incorporated in the state of Delaware on March 16, 2017. The Company is a clinical-stage biotechnology company leveraging a deep understanding of immunobiology to develop novel therapeutics to treat severe autoimmune and inflammatory (immuno-inflammatory), disorders with high unmet medical need. The Company’s strategy is focused on advancing the clinical development of its product candidates, including potentially pursuing additional indications and acquiring new product candidates and platforms to expand its pipeline. The Company intends to commercialize its product candidates either independently or through partnerships or otherwise monetize its pipeline through strategic transactions. The Company's current clinical-stage product candidates consist of EQ101, EQ102 and itolizumab (EQ001). EQ101 and EQ102 are synthetic peptides engineered to specifically inhibit key disease-driving, clinically validated cytokine targets aimed at addressing unmet needs across a range of immuno-inflammatory indications. EQ101 is a first-in class, selective, tri-specific inhibitor of IL-2, IL-9 and IL-15, and EQ102 is a first-in class, selective, bi-specific inhibitor of IL-15 and IL-21. Itolizumab (EQ001) is a first-in-class monoclonal antibody that selectively targets the immune checkpoint receptor CD6, which plays a central role in the modulation of effector T cell, or Teff cell, activity and trafficking that drives a number of immuno-inflammatory diseases across multiple therapeutic areas. The Company's novel and differentiated pipeline of first-in-class immunology assets has the potential to address unmet medical needs in numerous areas, including dermatology, gastroenterology, transplant science, hematology, rheumatology, oncology and pulmonology. From inception through December 31, 2022, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing rights to itolizumab (EQ001), conducting non-clinical research, filing three Investigational New Drug applications (INDs), conducting clinical development of the Company's product candidates, conducting business development activities such as the acquisition of Bioniz Therapeutics, Inc. (Bioniz), the Asset Purchase Agreement with Ono Pharmaceutical Co., Ltd. (Ono) and other transactions not completed, and the general and administrative activities associated with operating a public company. Liquidity and Business Risks As of December 31, 2022, the Company had $71.0 million in cash, cash equivalents and short-term investments. The Company has incurred significant operating losses and negative cash flows from operations. The Company expects to use its cash, cash equivalents, and short-term investments to fund research and development of its product candidates, for potentially acquiring and conducting research and development of new products, and for working capital and other general corporate purposes. The Company does not expect to generate any revenues from product sales unless and until the Company successfully completes development and obtains regulatory approval of any of its product candidates, which is unlikely to happen within the next 12 months, if ever. Accordingly, until such time as the Company can generate significant revenue from sales of its product candidates, if ever, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, and collaboration and license agreements, such as its Asset Purchase Agreement with Ono. However, the Company may not be able to secure additional financing or enter into such other arrangements in a timely manner or on favorable terms, if at all. As a result of the conflict between Russia and Ukraine, bank failures, inflationary pressures on the economy and monetary policy responses taken by government agencies and other macroeconomic factors, the global credit and financial markets have experienced extreme volatility, including diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth and uncertainty about economic stability. There can be no assurance that further deterioration in credit and financial markets and confidence in economic conditions will not occur. If equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult to obtain, more costly and/or more dilutive. The Company’s failure to raise capital or enter into such other arrangements when needed would have a negative impact on the Company’s financial condition and could force the Company to delay, reduce or terminate its research and development programs or other operations, or grant rights to develop and market product candidates that the Company would otherwise prefer to develop and market itself. Management believes that the Company’s cash, cash equivalents and short-term investments as of December 31, 2022 will be sufficient to fund operations for at least the next 12 months from the date this Annual Report on Form 10-K is filed with the Securities and Exchange Commission (SEC). Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the SEC. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) promulgated by the Financial Accounting Standards Board (FASB). Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Foreign Currency Translation The Company’s wholly-owned subsidiary in Australia uses its local currency as its functional currency. Assets and liabilities are translated into U.S. dollars at quarter-end exchange rates and revenues and expenses are translated at average exchange rates during the year-to-date periods. Foreign currency translation adjustments for the reported periods are included in accumulated other comprehensive income in the Company’s consolidated statements of comprehensive loss, and the cumulative effect is included in the stockholders’ equity section of the Company’s consolidated balance sheets. Recently Issued and Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments, which will require a reporting entity to use a new forward-looking impairment model for most financial assets that generally will result in the earlier recognition of allowances for losses. The ASU, along with related amendments, revised the measurement of credit losses for financial assets measured at amortized cost from an incurred loss to an expected loss methodology. The ASU affected receivables, debt securities, net investment in leases, and most other financial assets that represent a right to receive cash. The Company adopted this standard effective January 1, 2022 using the modified retrospective approach. Due to the nature of the Company's investment portfolio, the adoption of the guidance did not have a material effect on the Company's consolidated financial statements and no allowance was recorded for expected credit losses. From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that are adopted by the Company as of the specified effective date. The Company has evaluated recently issued pronouncements and does not believe any will have a material impact on the Company's consolidated financial statements or related financial statement disclosures. Other accounting standard updates effective for interim and annual periods beginning after December 31, 2022 are not expected to have a material impact on the Company’s financial position, results of operations or cash flows.

Equillium, Inc. (the Company) was incorporated in the state of Delaware on March 16, 2017. The Company is a clinical-stage biotechnology company leveraging a deep understanding of immunobiology to develop novel therapeutics to treat severe autoimmune and inflammatory (immuno-inflammatory), disorders with high unmet medical need. The Company’s strategy is focused on advancing the clinical development of its product candidates, including potentially pursuing additional indications and acquiring new product candidates and platforms to expand its pipeline. The Company intends to commercialize its product candidates either independently or through partnerships or otherwise monetize its pipeline through strategic transactions.

The Company's current clinical-stage product candidates consist of EQ101, EQ102 and itolizumab (EQ001). EQ101 and EQ102 are synthetic peptides engineered to specifically inhibit key disease-driving, clinically validated cytokine targets aimed at addressing unmet needs across a range of immuno-inflammatory indications. EQ101 is a first-in class, selective, tri-specific inhibitor of IL-2, IL-9 and IL-15, and EQ102 is a first-in class, selective, bi-specific inhibitor of IL-15 and IL-21. Itolizumab (EQ001) is a first-in-class monoclonal antibody that selectively targets the immune checkpoint receptor CD6, which plays a central role in the modulation of effector T cell, or Teff cell, activity and trafficking that drives a number of immuno-inflammatory diseases across multiple therapeutic areas. The Company's novel and differentiated pipeline of first-in-class immunology assets has the potential to address unmet medical needs in numerous areas, including dermatology, gastroenterology, transplant science, hematology, rheumatology, oncology and pulmonology.

From inception through December 31, 2022, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing rights to itolizumab (EQ001), conducting non-clinical research, filing three Investigational New Drug applications (INDs), conducting clinical development of the Company's product candidates, conducting business development activities such as the acquisition of Bioniz Therapeutics, Inc. (Bioniz), the Asset Purchase Agreement with Ono Pharmaceutical Co., Ltd. (Ono) and other transactions not completed, and the general and administrative activities associated with operating a public company.

As of December 31, 2022, the Company had $71.0 million in cash, cash equivalents and short-term investments. The Company has incurred significant operating losses and negative cash flows from operations. The Company expects to use its cash, cash equivalents, and short-term investments to fund research and development of its product candidates, for potentially acquiring and conducting research and development of new products, and for working capital and other general corporate purposes. The Company does not expect to generate any revenues from product sales unless and until the Company successfully completes development and obtains regulatory approval of any of its product candidates, which is unlikely to happen within the next 12 months, if ever. Accordingly, until such time as the Company can generate significant revenue from sales of its product candidates, if ever, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, and collaboration and license agreements, such as its Asset Purchase Agreement with Ono. However, the Company may not be able to secure additional financing or enter into such other arrangements in a timely manner or on favorable terms, if at all. As a result of the conflict between Russia and Ukraine, bank failures, inflationary pressures on the economy and monetary policy responses taken by government agencies and other macroeconomic factors, the global credit and financial markets have experienced extreme volatility, including diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth and uncertainty about economic stability. There can be no assurance that further deterioration in credit and financial markets and confidence in economic conditions will not occur. If equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult to obtain, more costly and/or more dilutive. The Company’s failure to raise capital or enter into such other arrangements when needed would have a negative impact on the Company’s financial condition and could force the Company to delay, reduce or terminate its research and development programs or other operations, or grant rights to develop and market product candidates that the Company would otherwise prefer to develop and market itself. Management believes that the Company’s cash, cash equivalents and short-term investments as of December 31, 2022 will be sufficient to fund operations for at least the next 12 months from the date this Annual Report on Form 10-K is filed with the Securities and Exchange Commission (SEC).

The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the SEC. Any reference in these notes to applicable guidance

is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) promulgated by the Financial Accounting Standards Board (FASB).

The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.

The Company’s wholly-owned subsidiary in Australia uses its local currency as its functional currency. Assets and liabilities are translated into U.S. dollars at quarter-end exchange rates and revenues and expenses are translated at average exchange rates during the year-to-date periods. Foreign currency translation adjustments for the reported periods are included in accumulated other comprehensive income in the Company’s consolidated statements of comprehensive loss, and the cumulative effect is included in the stockholders’ equity section of the Company’s consolidated balance sheets.

Recently Issued and Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments, which will require a reporting entity to use a new forward-looking impairment model for most financial assets that generally will result in the earlier recognition of allowances for losses. The ASU, along with related amendments, revised the measurement of credit losses for financial assets measured at amortized cost from an incurred loss to an expected loss methodology. The ASU affected receivables, debt securities, net investment in leases, and most other financial assets that represent a right to receive cash. The Company adopted this standard effective January 1, 2022 using the modified retrospective approach. Due to the nature of the Company's investment portfolio, the adoption of the guidance did not have a material effect on the Company's consolidated financial statements and no allowance was recorded for expected credit losses.