<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:a5bb88b5-88d1-4b41-a49b-1b380a8c2427,g:d58d4a1e-3a61-4446-8f20-6935b8d214a5-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:flks="http://www.flex-pharma.com/20221231" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2020-01-21" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.flex-pharma.com/20221231">
  <xs:import namespace="http://fasb.org/srt/2022" schemaLocation="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2022" schemaLocation="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd"/>
  <xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="http://www.xbrl.org/2003/xlink-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2022" schemaLocation="https://xbrl.sec.gov/dei/2022/dei-2022.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20221231_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20221231_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20221231_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20221231_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="COVERPAGE" roleURI="http://www.flex-pharma.com/role/COVERPAGE">
        <link:definition>0000001 - Document - COVER PAGE</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AUDITINFORMATION" roleURI="http://www.flex-pharma.com/role/AUDITINFORMATION">
        <link:definition>0000002 - Document - AUDIT INFORMATION</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONSOLIDATEDBALANCESHEETS" roleURI="http://www.flex-pharma.com/role/CONSOLIDATEDBALANCESHEETS">
        <link:definition>0000003 - Statement - CONSOLIDATED BALANCE SHEETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONSOLIDATEDBALANCESHEETSParenthetical" roleURI="http://www.flex-pharma.com/role/CONSOLIDATEDBALANCESHEETSParenthetical">
        <link:definition>0000004 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONSOLIDATEDSTATEMENTSOFOPERATIONS" roleURI="http://www.flex-pharma.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS">
        <link:definition>0000005 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONSOLIDATEDSTATEMENTSOFCASHFLOWS" roleURI="http://www.flex-pharma.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS">
        <link:definition>0000006 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYDEFICIT" roleURI="http://www.flex-pharma.com/role/CONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYDEFICIT">
        <link:definition>0000007 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ORGANIZATIONANDOPERATIONS" roleURI="http://www.flex-pharma.com/role/ORGANIZATIONANDOPERATIONS">
        <link:definition>0000008 - Disclosure - ORGANIZATION AND OPERATIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BASISOFPRESENTATIONANDSIGNIFICANTACCOUNTINGPOLICIES" roleURI="http://www.flex-pharma.com/role/BASISOFPRESENTATIONANDSIGNIFICANTACCOUNTINGPOLICIES">
        <link:definition>0000009 - Disclosure - BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GRANTSRECEIVABLE" roleURI="http://www.flex-pharma.com/role/GRANTSRECEIVABLE">
        <link:definition>0000010 - Disclosure - GRANTS RECEIVABLE</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PREPAIDEXPENSESANDOTHERCURRENTASSETS" roleURI="http://www.flex-pharma.com/role/PREPAIDEXPENSESANDOTHERCURRENTASSETS">
        <link:definition>0000011 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="COMMITMENTSANDCONTINGENCIES" roleURI="http://www.flex-pharma.com/role/COMMITMENTSANDCONTINGENCIES">
        <link:definition>0000012 - Disclosure - COMMITMENTS AND CONTINGENCIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FAIRVALUEOFFINANCIALINSTRUMENTS" roleURI="http://www.flex-pharma.com/role/FAIRVALUEOFFINANCIALINSTRUMENTS">
        <link:definition>0000013 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="STOCKHOLDERSEQUITY" roleURI="http://www.flex-pharma.com/role/STOCKHOLDERSEQUITY">
        <link:definition>0000014 - Disclosure - STOCKHOLDERS' EQUITY</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EQUITYBASEDCOMPENSATION" roleURI="http://www.flex-pharma.com/role/EQUITYBASEDCOMPENSATION">
        <link:definition>0000015 - Disclosure - EQUITY-BASED COMPENSATION</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="INCOMETAX" roleURI="http://www.flex-pharma.com/role/INCOMETAX">
        <link:definition>0000016 - Disclosure - INCOME TAX</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SUBSEQUENTEVENTS" roleURI="http://www.flex-pharma.com/role/SUBSEQUENTEVENTS">
        <link:definition>0000017 - Disclosure - SUBSEQUENT EVENTS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BASISOFPRESENTATIONANDSIGNIFICANTACCOUNTINGPOLICIESPolicies" roleURI="http://www.flex-pharma.com/role/BASISOFPRESENTATIONANDSIGNIFICANTACCOUNTINGPOLICIESPolicies">
        <link:definition>0000018 - Disclosure - BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PREPAIDEXPENSESANDOTHERCURRENTASSETSTables" roleURI="http://www.flex-pharma.com/role/PREPAIDEXPENSESANDOTHERCURRENTASSETSTables">
        <link:definition>0000019 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EQUITYBASEDCOMPENSATIONTables" roleURI="http://www.flex-pharma.com/role/EQUITYBASEDCOMPENSATIONTables">
        <link:definition>0000020 - Disclosure - EQUITY-BASED COMPENSATION (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="INCOMETAXTables" roleURI="http://www.flex-pharma.com/role/INCOMETAXTables">
        <link:definition>0000021 - Disclosure - INCOME TAX (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ORGANIZATIONANDOPERATIONSDetails" roleURI="http://www.flex-pharma.com/role/ORGANIZATIONANDOPERATIONSDetails">
        <link:definition>0000022 - Disclosure - ORGANIZATION AND OPERATIONS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="BASISOFPRESENTATIONANDSIGNIFICANTACCOUNTINGPOLICIESDetails" roleURI="http://www.flex-pharma.com/role/BASISOFPRESENTATIONANDSIGNIFICANTACCOUNTINGPOLICIESDetails">
        <link:definition>0000023 - Disclosure - BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GRANTSRECEIVABLEDetails" roleURI="http://www.flex-pharma.com/role/GRANTSRECEIVABLEDetails">
        <link:definition>0000024 - Disclosure - GRANTS RECEIVABLE (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PREPAIDEXPENSESANDOTHERCURRENTASSETSScheduleofPrepaidExpensesandOtherCurrentAssetsDetails" roleURI="http://www.flex-pharma.com/role/PREPAIDEXPENSESANDOTHERCURRENTASSETSScheduleofPrepaidExpensesandOtherCurrentAssetsDetails">
        <link:definition>0000025 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS - Schedule of Prepaid Expenses and Other Current Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="COMMITMENTSANDCONTINGENCIESDetails" roleURI="http://www.flex-pharma.com/role/COMMITMENTSANDCONTINGENCIESDetails">
        <link:definition>0000026 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="STOCKHOLDERSEQUITYNarrativeDetails" roleURI="http://www.flex-pharma.com/role/STOCKHOLDERSEQUITYNarrativeDetails">
        <link:definition>0000027 - Disclosure - STOCKHOLDERS' EQUITY - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EQUITYBASEDCOMPENSATIONNarrativeDetails" roleURI="http://www.flex-pharma.com/role/EQUITYBASEDCOMPENSATIONNarrativeDetails">
        <link:definition>0000028 - Disclosure - EQUITY-BASED COMPENSATION - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EQUITYBASEDCOMPENSATIONScheduleofFairValueAssumptionsDetails" roleURI="http://www.flex-pharma.com/role/EQUITYBASEDCOMPENSATIONScheduleofFairValueAssumptionsDetails">
        <link:definition>0000029 - Disclosure - EQUITY-BASED COMPENSATION - Schedule of Fair Value Assumptions (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EQUITYBASEDCOMPENSATIONSummaryofStockOptionActivityDetails" roleURI="http://www.flex-pharma.com/role/EQUITYBASEDCOMPENSATIONSummaryofStockOptionActivityDetails">
        <link:definition>0000030 - Disclosure - EQUITY-BASED COMPENSATION - Summary of Stock Option Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="INCOMETAXScheduleofEffectiveIncomeTaxRateReconciliationDetails" roleURI="http://www.flex-pharma.com/role/INCOMETAXScheduleofEffectiveIncomeTaxRateReconciliationDetails">
        <link:definition>0000031 - Disclosure - INCOME TAX - Schedule of Effective Income Tax Rate Reconciliation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="INCOMETAXScheduleofDeferredTaxAssetsandLiabilitiesDetails" roleURI="http://www.flex-pharma.com/role/INCOMETAXScheduleofDeferredTaxAssetsandLiabilitiesDetails">
        <link:definition>0000032 - Disclosure - INCOME TAX - Schedule of Deferred Tax Assets and Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="INCOMETAXNarrativeDetails" roleURI="http://www.flex-pharma.com/role/INCOMETAXNarrativeDetails">
        <link:definition>0000033 - Disclosure - INCOME TAX - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SUBSEQUENTEVENTSDetails" roleURI="http://www.flex-pharma.com/role/SUBSEQUENTEVENTSDetails">
        <link:definition>0000034 - Disclosure - SUBSEQUENT EVENTS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="flks_StockIssuanceCostsAccruedAndAmortized" abstract="false" name="StockIssuanceCostsAccruedAndAmortized" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_CertainEmployeesMember" abstract="true" name="CertainEmployeesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="flks_RevenueFromGrantsAwardTerm" abstract="false" name="RevenueFromGrantsAwardTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="flks_StockIssuedDuringPeriodValueWarrantsExercised" abstract="false" name="StockIssuedDuringPeriodValueWarrantsExercised" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_EquityIncentivePlan2015Member" abstract="true" name="EquityIncentivePlan2015Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="flks_SaleOfStockPercentageOfShareInTransaction" abstract="false" name="SaleOfStockPercentageOfShareInTransaction" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="flks_RevenueFromGrantsRevenueSharingPaymentsContinuedPaymentsPercentOfNetSales" abstract="false" name="RevenueFromGrantsRevenueSharingPaymentsContinuedPaymentsPercentOfNetSales" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="flks_AccruedExpensesAndOtherCurrentLiabilities" abstract="false" name="AccruedExpensesAndOtherCurrentLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_UniversityOfUtahResearchFoundationMember" abstract="true" name="UniversityOfUtahResearchFoundationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="flks_RevenueFromGrantsCumulativeDisbursement" abstract="false" name="RevenueFromGrantsCumulativeDisbursement" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_AuditInformationAbstract" abstract="true" name="AuditInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="flks_PrepaidClinicalTrialExpense" abstract="false" name="PrepaidClinicalTrialExpense" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_EffectiveIncomeTaxRateReconciliationTrueUpsPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationTrueUpsPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="flks_RevenueFromGrantsMaximumAward" abstract="false" name="RevenueFromGrantsMaximumAward" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_StockIssuedDuringPeriodSharesWarrantsExercised" abstract="false" name="StockIssuedDuringPeriodSharesWarrantsExercised" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="flks_AtTheMarketEquityOfferingProgramMember" abstract="true" name="AtTheMarketEquityOfferingProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="flks_AtTheMarketOfferingAgreementMember" abstract="true" name="AtTheMarketOfferingAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="flks_PurchaseAgreementMember" abstract="true" name="PurchaseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="flks_CapitalizedResearchAndDevelopmentCosts" abstract="false" name="CapitalizedResearchAndDevelopmentCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="flks_WarrantsAndRightsExercisableTerm" abstract="false" name="WarrantsAndRightsExercisableTerm" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
</xs:schema>
