Organization and Accounting Pronouncements	12 Months Ended
Dec. 31, 2021
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 deep understanding of immunology to develop novel products to treat severe autoimmune and inflammatory disorders with high unmet medical need. From inception through December 31, 2021, 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 initial product candidate, itolizumab (EQ001), conducting business development activities, and the general and administrative activities associated with operating a public company. In addition, the Company has not generated revenues from its principal operations and the sales and income potential of its business is unproven. Liquidity and Business Risks As of December 31, 2021, the Company had $80.7 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 itolizumab (EQ001), 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 itolizumab (EQ001) or any future product candidate, 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. 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 COVID-19 pandemic and actions taken to slow its spread, the global credit and financial markets have experienced extreme volatility, including diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth, increases in unemployment rates 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, 2021 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 COVID-19 outbreak in the United States and the rest of the world has caused disruptions to the Company’s business, which may delay results of the Company’s clinical trials and adversely impact the Company’s business. The Company cannot predict how legal and regulatory responses to concerns about COVID-19 or other major public health issues will impact the Company’s business, nor can it predict potential adverse impacts related to the availability of capital to fund the Company’s operations. Additionally, the Company’s workforce and outside consultants may also be affected, which could result in an adverse impact on the Company’s ability to conduct business. Any of these factors, alone or in combination with others, could harm the Company’s business, results of operations, financial condition or liquidity. However, the magnitude, timing, and duration of any such potential financial impacts cannot be reasonably estimated at this time. 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 subsidiary in Australia. 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 loss 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. Realized and unrealized gains and losses denominated in foreign currencies are recorded in operating expenses in the Company’s consolidated statements of operations. For the years ended December 31, 2021 and 2020, net realized and unrealized gain totaled $0.2 million and, net realized and unrealized loss of $0.3 million, respectively. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which supersedes ASC 840, Leases. ASU 2016-02 establishes ASC 842, Leases, and provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification determines whether lease expense is recognized based on an effective interest method for finance leases or on a straight-line basis over the term of the lease for operating leases. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases. The Company adopted ASU 2016-02 and ASC 842 using the modified retrospective approach with an effective date of January 1, 2021. Periods prior to January 1, 2021 have not been restated for the adoption of ASC 842 and continue to reflect the accounting treatment of leases in accordance with ASC 840. In connection with the adoption, the Company elected the package of practical expedients to not reassess prior conclusions about lease identification, lease classification and capitalized indirect costs. The Company did not elect the use of hindsight practical expedient. Upon adoption, effective January 1, 2021, the Company recognized operating lease right-of-use assets of $0.5 million and operating lease liabilities of $0.5 million. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The amendments in this ASU are effective for the Company on January 1, 2021. The adoption of this standard did not have a material impact on the Company's consolidated financial statements. Recent Accounting Pronouncements not adopted 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 standard and other related subsequently issued ASUs will be effective for the Company for annual periods beginning after December 15, 2022, with early adoption permitted beginning in 2019. The Company is currently evaluating the impact that the adoption of the standard and other related subsequently issued ASUs will have on its consolidated financial statements and accompanying footnotes. Other accounting standard updates effective for interim and annual periods beginning after December 31, 2021 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 deep understanding of immunology to develop novel products to treat severe autoimmune and inflammatory disorders with high unmet medical need.

From inception through December 31, 2021, 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 initial product candidate, itolizumab (EQ001), conducting business development activities, and the general and administrative activities associated with operating a public company. In addition, the Company has not generated revenues from its principal operations and the sales and income potential of its business is unproven.

As of December 31, 2021, the Company had $80.7 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 itolizumab (EQ001), 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 itolizumab (EQ001) or any future product candidate, 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. 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 COVID-19 pandemic and actions taken to slow its spread, the global credit and financial markets have experienced extreme volatility, including diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth, increases in unemployment rates 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, 2021 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 COVID-19 outbreak in the United States and the rest of the world has caused disruptions to the Company’s business, which may delay results of the Company’s clinical trials and adversely impact the Company’s business. The Company cannot predict how legal and regulatory responses to concerns about COVID-19 or other major public health issues will impact the Company’s business, nor can it predict potential adverse impacts related to the availability of capital to fund the Company’s operations. Additionally, the Company’s workforce and outside consultants may also be affected, which could result in an adverse impact on the Company’s ability to conduct business. Any of these factors, alone or in combination with others, could harm the Company’s business, results of operations, financial condition or liquidity. However, the magnitude, timing, and duration of any such potential financial impacts cannot be reasonably estimated at this time.

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 subsidiary in Australia. 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 loss 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. Realized and unrealized gains and losses denominated in foreign currencies are recorded in operating expenses in the Company’s consolidated statements of operations. For the years ended December 31, 2021 and 2020, net realized and unrealized gain totaled $0.2 million and, net realized and unrealized loss of $0.3 million, respectively.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which supersedes ASC 840, Leases. ASU 2016-02 establishes ASC 842, Leases, and provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification determines whether lease expense is recognized based on an effective interest method for finance leases or on a straight-line basis over the term of the lease for operating leases. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases. The Company adopted ASU 2016-02 and ASC 842 using the modified retrospective approach with an effective date of January 1, 2021. Periods prior to January 1, 2021 have not been restated for the adoption of ASC 842 and continue to reflect the accounting treatment of leases in accordance with ASC 840. In connection with the adoption, the Company elected the package of practical expedients to not reassess prior conclusions about lease identification, lease classification and capitalized indirect costs. The Company did not elect the use of hindsight practical expedient. Upon adoption, effective January 1, 2021, the Company recognized operating lease right-of-use assets of $0.5 million and operating lease liabilities of $0.5 million.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The amendments in this ASU are effective for the Company on January 1, 2021. The adoption of this standard did not have a material impact on the Company's consolidated financial statements.

Recent Accounting Pronouncements not adopted

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 standard and other related subsequently issued ASUs will be effective for the Company for annual periods beginning after December 15, 2022, with early adoption permitted beginning in 2019. The Company is currently evaluating the impact that the adoption of the standard and other related subsequently issued ASUs will have on its consolidated financial statements and accompanying footnotes.