

<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<xsd:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.flex-pharma.com/20170331" xmlns:flks="http://www.flex-pharma.com/20170331" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:import namespace="http://fasb.org/us-gaap/2016-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/us-roles/2016-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2016/elts/us-roles-2016-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/us-types/2016-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2016/elts/us-types-2016-01-31.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/arcrole/fact-explanatoryFact" schemaLocation="http://www.xbrl.org/lrr/arcrole/factExplanatory-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/role/negated" schemaLocation="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/role/net" schemaLocation="http://www.xbrl.org/lrr/role/net-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/dtr/type/numeric" schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd" />
  <xsd:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/country/2016-01-31" schemaLocation="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/currency/2016-01-31" schemaLocation="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/dei/2014-01-31" schemaLocation="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/exch/2016-01-31" schemaLocation="http://xbrl.sec.gov/exch/2016/exch-2016-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/invest/2013-01-31" schemaLocation="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/naics/2011-01-31" schemaLocation="http://xbrl.sec.gov/naics/2011/naics-2011-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/sic/2011-01-31" schemaLocation="http://xbrl.sec.gov/sic/2011/sic-2011-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/stpr/2011-01-31" schemaLocation="http://xbrl.sec.gov/stpr/2011/stpr-2011-01-31.xsd" />
  <xsd:annotation>
    <xsd:appinfo>
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20170331_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20170331_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20170331_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="flks-20170331_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple" />
      <link:roleType id="AccruedExpensesAndOtherCurrentLiabilities" roleURI="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilities">
        <link:definition>2119100 - Disclosure - Accrued expenses and other current liabilities</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="AccruedExpensesAndOtherCurrentLiabilitiesDetails" roleURI="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilitiesDetails">
        <link:definition>2419402 - Disclosure - Accrued expenses and other current 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="AccruedExpensesAndOtherCurrentLiabilitiesTables" roleURI="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilitiesTables">
        <link:definition>2319301 - Disclosure - Accrued expenses and other current liabilities (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="CashEquivalentsAndMarketableSecurities" roleURI="http://www.flex-pharma.com/role/CashEquivalentsAndMarketableSecurities">
        <link:definition>2113100 - Disclosure - Cash equivalents and marketable securities</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="CashEquivalentsAndMarketableSecuritiesDetails" roleURI="http://www.flex-pharma.com/role/CashEquivalentsAndMarketableSecuritiesDetails">
        <link:definition>2413402 - Disclosure - Cash equivalents and marketable securities (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="CashEquivalentsAndMarketableSecuritiesTables" roleURI="http://www.flex-pharma.com/role/CashEquivalentsAndMarketableSecuritiesTables">
        <link:definition>2313301 - Disclosure - Cash equivalents and marketable securities (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="CommonStock" roleURI="http://www.flex-pharma.com/role/CommonStock">
        <link:definition>2122100 - Disclosure - Common stock</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="CommonStockNarrativeDetails" roleURI="http://www.flex-pharma.com/role/CommonStockNarrativeDetails">
        <link:definition>2422402 - Disclosure - Common stock - 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="CommonStockRestrictedCommonStockActivityDetails" roleURI="http://www.flex-pharma.com/role/CommonStockRestrictedCommonStockActivityDetails">
        <link:definition>2422403 - Disclosure - Common stock - Restricted common stock 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="CommonStockTables" roleURI="http://www.flex-pharma.com/role/CommonStockTables">
        <link:definition>2322301 - Disclosure - Common stock (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="CondensedConsolidatedBalanceSheetsUnaudited" roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedBalanceSheetsUnaudited">
        <link:definition>1001000 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited)</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="CondensedConsolidatedBalanceSheetsUnauditedParenthetical" roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedBalanceSheetsUnauditedParenthetical">
        <link:definition>1001501 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (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="CondensedConsolidatedStatementsOfCashFlowsUnaudited" roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited">
        <link:definition>1005000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)</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="CondensedConsolidatedStatementsOfComprehensiveLossUnaudited" roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfComprehensiveLossUnaudited">
        <link:definition>1004000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited)</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="CondensedConsolidatedStatementsOfOperationsUnaudited" roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfOperationsUnaudited">
        <link:definition>1002000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited)</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="DocumentAndEntityInformation" roleURI="http://www.flex-pharma.com/role/DocumentAndEntityInformation">
        <link:definition>0001000 - Document - Document and Entity 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="FairValueMeasurements" roleURI="http://www.flex-pharma.com/role/FairValueMeasurements">
        <link:definition>2110100 - Disclosure - Fair value measurements</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="FairValueMeasurementsDetails" roleURI="http://www.flex-pharma.com/role/FairValueMeasurementsDetails">
        <link:definition>2410402 - Disclosure - Fair value measurements (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="FairValueMeasurementsTables" roleURI="http://www.flex-pharma.com/role/FairValueMeasurementsTables">
        <link:definition>2310301 - Disclosure - Fair value measurements (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="IncomeTaxes" roleURI="http://www.flex-pharma.com/role/IncomeTaxes">
        <link:definition>2124100 - Disclosure - Income taxes</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="IncomeTaxesDetails" roleURI="http://www.flex-pharma.com/role/IncomeTaxesDetails">
        <link:definition>2424401 - Disclosure - Income taxes (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="Inventory" roleURI="http://www.flex-pharma.com/role/Inventory">
        <link:definition>2116100 - Disclosure - Inventory</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="InventoryDetails" roleURI="http://www.flex-pharma.com/role/InventoryDetails">
        <link:definition>2416402 - Disclosure - Inventory (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="InventoryTables" roleURI="http://www.flex-pharma.com/role/InventoryTables">
        <link:definition>2316301 - Disclosure - Inventory (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="NetLossPerShare" roleURI="http://www.flex-pharma.com/role/NetLossPerShare">
        <link:definition>2125100 - Disclosure - Net loss per share</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="NetLossPerShareDetails" roleURI="http://www.flex-pharma.com/role/NetLossPerShareDetails">
        <link:definition>2425402 - Disclosure - Net loss per share (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="NetLossPerShareTables" roleURI="http://www.flex-pharma.com/role/NetLossPerShareTables">
        <link:definition>2325301 - Disclosure - Net loss per share (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="OrganizationAndOperations" roleURI="http://www.flex-pharma.com/role/OrganizationAndOperations">
        <link:definition>2101100 - 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="OrganizationAndOperationsDetails" roleURI="http://www.flex-pharma.com/role/OrganizationAndOperationsDetails">
        <link:definition>2401401 - 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="SegmentInformation" roleURI="http://www.flex-pharma.com/role/SegmentInformation">
        <link:definition>2126100 - Disclosure - Segment 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="SegmentInformationDetails" roleURI="http://www.flex-pharma.com/role/SegmentInformationDetails">
        <link:definition>2426402 - Disclosure - Segment Information (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="SegmentInformationTables" roleURI="http://www.flex-pharma.com/role/SegmentInformationTables">
        <link:definition>2326301 - Disclosure - Segment Information (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="StockBasedCompensation" roleURI="http://www.flex-pharma.com/role/StockBasedCompensation">
        <link:definition>2123100 - Disclosure - Stock-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="StockBasedCompensationNarrativeDetails" roleURI="http://www.flex-pharma.com/role/StockBasedCompensationNarrativeDetails">
        <link:definition>2423402 - Disclosure - Stock-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="StockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails" roleURI="http://www.flex-pharma.com/role/StockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails">
        <link:definition>2423404 - Disclosure - Stock-based compensation - Summary of stock-based compensation expense (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="StockBasedCompensationSummaryOfStockOptionActivityDetails" roleURI="http://www.flex-pharma.com/role/StockBasedCompensationSummaryOfStockOptionActivityDetails">
        <link:definition>2423403 - Disclosure - Stock-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="StockBasedCompensationTables" roleURI="http://www.flex-pharma.com/role/StockBasedCompensationTables">
        <link:definition>2323301 - Disclosure - Stock-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="SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements" roleURI="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements">
        <link:definition>2104100 - Disclosure - Summary of significant accounting policies and recent accounting pronouncements</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="SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsNarrativeDetails" roleURI="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsNarrativeDetails">
        <link:definition>2404402 - Disclosure - Summary of significant accounting policies and recent accounting pronouncements - 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="SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies" roleURI="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies">
        <link:definition>2204201 - Disclosure - Summary of significant accounting policies and recent accounting pronouncements (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xsd:appinfo>
  </xsd:annotation>
  <xsd:element abstract="true" id="flks_AccountingStandardsUpdate201609Member" name="AccountingStandardsUpdate201609Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="flks_AccruedExpensesAndOtherCurrentLiabilities" name="AccruedExpensesAndOtherCurrentLiabilities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="flks_AccruedResearchAndDevelopmentExpenseCurrent" name="AccruedResearchAndDevelopmentExpenseCurrent" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="flks_ConsumerOperationsMember" name="ConsumerOperationsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="flks_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="flks_DrugDevelopmentMember" name="DrugDevelopmentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="flks_EquityIncentivePlan2015Member" name="EquityIncentivePlan2015Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="flks_FlexPharmaInc.2014EquityIncentivePlanMember" name="FlexPharmaInc.2014EquityIncentivePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="flks_NonemployeeConsultantsandAdvisersMember" name="NonemployeeConsultantsandAdvisersMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="flks_ProceedsFromSaleOfRestrictedCommonStock" name="ProceedsFromSaleOfRestrictedCommonStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="flks_PropertyAndEquipmentPurchasesInAccruedExpense" name="PropertyAndEquipmentPurchasesInAccruedExpense" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="flks_RevenueRecognitionRefundPeriod" name="RevenueRecognitionRefundPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
</xsd:schema>