Total operating expenses were $35.5 million or 155.1% of net revenues for the second quarter of 2021, compared with $16.3 million or 102.3% of net revenues for the second quarter of 2020. The increase was primarily due to higher sales and marketing investments in demand generation, costs associated with the Eargo 5 launch, personnel investments to scale the organization for growth, stock-based compensation and expenses related to being a public company.
Sales and marketing expenses were $21.9 million or 95.7% of net revenues for the second quarter of 2021, compared with $10.8 million or 68.0% of net revenues for the second quarter of 2020.
Research and development expenses were $5.2 million or 22.5% of net revenues for the second quarter of 2021, compared with $2.2 million or 13.9% of net revenues for the second quarter of 2020.
General and administrative expenses were $8.4 million or 36.8% of net revenues for the second quarter of 2021, compared with $3.3 million or 20.5% of net revenues for the second quarter of 2020.
Excluding stock-based compensation expense, non-GAAP operating expenses were $30.4 million, including research and development expenses of $4.1 million, sales and marketing expenses of $20.0 million, and general and administrative expenses of $6.3 million. Please refer to the section below titled “Use of Non-GAAP Financial Measures” and the non-GAAP reconciliation tables at the end of this press release.
Net loss attributable to common stockholders for the second quarter of 2021 was ($19.3) million, or ($0.50) per share, compared to a net loss of ($6.6) million, or ($23.66) per share, for the second quarter of 2020. Excluding stock-based compensation expense, non-GAAP net loss attributable to common stockholders for the second quarter of 2021 was ($14.1) million, or ($0.36) per share, compared to a non-GAAP net loss of ($6.1) million, or ($21.97) per share for the same period in 2020.
Cash and cash equivalents were $179.4 million as of June 30, 2021, compared to $212.2 million as of December 31, 2020.
Accounts receivable, net was $15.4 million as of June 30, 2021. The increase in accounts receivable from March 31, 2021 was primarily due to a claims audit by an insurance company that is our largest third-party payor, who accounted for approximately 80% of our gross accounts receivable as of June 30, 2021. During the audit, claims since March 1, 2021 have not been paid. The Company is in active discussions with the payor and continues to work toward conclusion of the audit.
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